Time Machine 1.1 sometimes deletes backups that should keep

About two years ago I was intrigued about the disparition of several Time Machine backups. After changing to a larger external backup disk, I've been trying to follow the behavior of Time Machine. Overall, it seems to be quite predictable, corresponding to what is explained in its window: mostly keeping hourly backups during 24 hours, then, from these, only keeping the first one in each day during 30 days, and then, from these remaining backups, only keeping one per week as "space" permits. Since the new backup partition is large (240% of the HD disk), it is still far from removing oldest backup(s) in order to free space. However, in my system, Time Machine has removed more backups, which should have been kept, in at least two occassions:

1. Several weeks ago, one month after having the system down for several days, two or three backups (specifically 2012-07-24-002423 and 2012-07-29-120258) that should be kept as weekly ones were deleted, possibly trying to resyncronize to a new day-of-week for the new series of weekly backups to keep.
2. Recently, and possibly related with heavy memory load giving 7 GB of swap, TM "got crazy" during two activations, deleting up to eight backups, both daily and weekly ones, which were far from being the oldest backups in the volume.

Has someone else observed this kind of behavior? What can be done to avoid it? If, as it seems, it is a bug in Time Machine, how can I notify Apple?

Since Time Machine seems to have a limit of 5 old backup deletions per activation, and given that occasionally strange (and dangerous) behavior, I think that Time Machine should warn when backups older than one month are deleted, and ask permission when 5 or more backups are going to be deleted (at least giving the user the possibility of configuring it so). We are talking here of data security, so some precautions should be allowed when destroying large quantities of data, which otherwise may not be recoverable.

The essential details follow:

Strings in recent system.log messages containing "deleted backup" (first & last groups are normal, there was no hourly backup to delete between them):

Oct 27 00:30:46 iMac com.apple.backupd[34391]: Deleted backup /Volumes/iMac HD Time Machine/Backups.backupdb/iMac/2012-09-27-002110: 120.20 GB now available

Oct 27 02:27:42 iMac com.apple.backupd[34677]: Deleted backup /Volumes/iMac HD Time Machine/Backups.backupdb/iMac/2012-03-22-232115: 132.85 GB now available

Oct 27 02:29:05 iMac com.apple.backupd[34677]: Deleted backup /Volumes/iMac HD Time Machine/Backups.backupdb/iMac/2012-04-06-000633: 143.17 GB now available

Oct 27 02:30:23 iMac com.apple.backupd[34677]: Deleted backup /Volumes/iMac HD Time Machine/Backups.backupdb/iMac/2012-09-28-002619: 146.29 GB now available

Oct 27 02:31:32 iMac com.apple.backupd[34677]: Deleted backup /Volumes/iMac HD Time Machine/Backups.backupdb/iMac/2012-09-30-004344: 149.48 GB now available

Oct 27 02:31:50 iMac com.apple.backupd[34677]: Deleted backup /Volumes/iMac HD Time Machine/Backups.backupdb/iMac/2012-10-03-000509: 152.58 GB now available

Oct 27 03:27:04 iMac com.apple.backupd[34860]: Deleted backup /Volumes/iMac HD Time Machine/Backups.backupdb/iMac/2012-10-08-001931: 155.64 GB now available

Oct 27 03:27:40 iMac com.apple.backupd[34860]: Deleted backup /Volumes/iMac HD Time Machine/Backups.backupdb/iMac/2012-10-14-003758: 159.26 GB now available

Oct 27 03:28:32 iMac com.apple.backupd[34860]: Deleted backup /Volumes/iMac HD Time Machine/Backups.backupdb/iMac/2012-10-22-002147: 162.48 GB now available

Oct 27 11:37:36 iMac com.apple.backupd[35839]: Deleted backup /Volumes/iMac HD Time Machine/Backups.backupdb/iMac/2012-10-26-104655: 153.98 GB now available

List of backups dates in the backup volume, and free space, taken from the terminal (after deletions: note that the backups marked in red should normally be kept):

iMac:~ admin$ ls /Volumes/iMac\ HD\ Time\ Machine/Backups.backupdb/iMac/

2011-10-01-061010 2012-05-31-093201 2012-10-20-002816

2011-10-09-005429 2012-06-07-002543 2012-10-21-021504

2011-10-16-001503 2012-06-14-005742 2012-10-23-004109

2011-10-23-002554 2012-06-21-001427 2012-10-24-002334

2011-11-05-001403 2012-06-28-001245 2012-10-25-002414

2011-11-12-004617 2012-07-05-002056 2012-10-26-002613

2011-11-19-000532 2012-07-12-002639 2012-10-26-012840

2011-11-26-000431 2012-07-19-005850 2012-10-27-012731

2011-12-03-000109 2012-08-05-002510 2012-10-27-032628

2011-12-10-003557 2012-08-12-002739 2012-10-27-042813

2011-12-17-002907 2012-08-19-005740 2012-10-27-052837

2011-12-24-001228 2012-09-03-110847 2012-10-27-062824

2011-12-31-002103 2012-09-10-123630 2012-10-27-113711

2012-01-07-005520 2012-09-17-002437 2012-10-27-123817

2012-01-14-000913 2012-09-24-002309 2012-10-27-133739

2012-01-21-005206 2012-09-29-011601 2012-10-27-143746

2012-01-28-000105 2012-10-01-001701 2012-10-27-153817

2012-02-04-022951 2012-10-02-010201 2012-10-27-163745

2012-02-12-210133 2012-10-04-000909 2012-10-27-173738

2012-02-24-002145 2012-10-07-112125 2012-10-27-183838

2012-03-02-002405 2012-10-09-001929 2012-10-27-193814

2012-03-09-003236 2012-10-10-002008 2012-10-27-203751

2012-03-16-002756 2012-10-11-001416 2012-10-27-213752

2012-03-30-014934 2012-10-12-004500 2012-10-27-223747

2012-04-19-004318 2012-10-13-012506 2012-10-27-233844

2012-04-26-012354 2012-10-15-003823 2012-10-28-011809

2012-05-03-003008 2012-10-16-002207 2012-10-28-013726

2012-05-10-004554 2012-10-17-002306 Latest

2012-05-17-011942 2012-10-18-002230

2012-05-24-001808 2012-10-19-002253

iMac:~ admin$ df

Filesystem 512-blocks Used Available Capacity Mounted on

/dev/disk0s2 914062528 585638424 327912104 65% /

devfs 226 226 0 100% /dev

map -hosts 0 0 0 100% /net

map auto_home 0 0 0 100% /home

/dev/disk1s4 2343750000 1980326912 363423088 85% /Volumes/iMac HD Time Machine

/dev/disk1s3 976562504 568072864 408489640 59% /Volumes/iMac HD SuperDuper!