Mail Search & Smart Folder bugs in Mavericks still not fixed in Yosemite?!

When Mavericks was introduced, Smart Folders and Search stopped working correctly for me, and for many many others. There were many threads about it, including a few fixes that would work for a short time - but always the problem would come back.

The problem:

Smart Folders would stop displaying all or some of the messages that they should, and Search within Mail would stop delivering all or some of the messages that it should. I am not discussing Maverick's problems with Gmail, but rather a different long-standing problem with plain IMAP accounts.

Temporary fixes that never stick:

A temporary fix that worked for a while is deleting the "Envelope Index" files in ~/Library/Mail/V2/MailData and letting Mail rebuild the index. But always the problem recurs in a matter of hours or occasionally a day or two. Using "rebuild" on invidual mailboxes would also fix it for a short while, but again the fix was always temporary. Another fix that would work for a short time is reindexing the mail folders in Spotlight, via Terminal -- but again the fix was always temporary.

Other symptoms:

1. Outside Mail, Spotlight has no problem finding the mail messages that it cannot find within Mail.

2. When deleting Envelope Index files and letting them rebuild when Mail is launched, temporary Envelope Index files are created (I assume this is normal) and not deleted at the end of the process (which I assume is not expected behavior).

3. And yes, this problem did not occur before Mavericks.

I am utterly astounded to see that the problem has not been fixed in Yosemite. For a day or two, I had some hope the problem was gone, because Mail was working correctly for a while, but no -- the problem is still there in exactly the same form. Exactly the same fixes work in exactly the same very temporary fashion.

And yes, I (and many others, I think) filed Mavericks bug reports about this.

With this message, I am mainly reality-checking to see if I am the only one (unless someone has a new magic solution to offer). I am really fed up. Can anyone suggest anything (besides switching to another Mail client -- I have reasons for needing to stick to Apple Mail).

Mac Pro 2008 & MacBook Pro 2013, Yosemite 10.10