WindowsME..
It could be that one of the delta updates did not install correctly or was missed during the update process.. or a different update version was applied somewhere in the past.... . Little things like that can and do change things dramatically...
(Delta updates are updates that do not replace the entire app or routine that is being updated but only replaces a part of the app or routine... which decreases the total download size of the update)
Apple switched to using Delta updates a while back and it seems sometimes different or incomplete or corrupted ones get installed which can cause issues down the road...
Just for further info on these types of problems...
Another example of this type of issue was the Prokit Issue a while back... when some people got one version of the Prokit installed and others got a different version installed and those that got the different version then had for example.. an issue saving in Logic... or Logic would crash unexpectedly when the user tried to save/load a project.... until they manually downloaded and installed a new replacement version of the Prokit that then fixed their issue. Using the automatic update feature in OS X did not fix the problem.. The User had to manually download and install a fresh copy of prokit to resolve the problem..Apple never truly explained how this could happen but happen it did and caused all kinds of problems that still go on today....
Here is a link to a thread relating to the Prokit issue...
https://discussions.apple.com/thread/3155576?start=0&tstart=0
and here is a link to one of the reports on how to fix it..
http://reviews.cnet.com/8301-13727_7-20096767-263/a-fix-for-logic-crashing-in-sn ow-leopard/
Note: many people never had this issue... nor even heard about it because, as like the GUI Lag problem.. not everyone is affected... and so those not affected never had to go through this process to fix it... but for the group of people who did have this issue, it was a nightmare, similar to the one going on at the moment with the GUI lag..
Finally,. here is the official Apple Support link for the Prokit fix...
http://support.apple.com/kb/TS3968