There are a few preferences like lowering undo steps, reducing autmation res and data, as well as emptying (Logic's)trash upon save which free up memory. If you open song information you can see what is taking up memory and what may be expendable. Cutting a region creates multiple regions so removing unused can really help to keep memory low. Leaving lots of room on your sytem drive and upping your RAM will also give you less problems. Committing edits (like if there is a passage with 200 regions and they all have fades on them-gluing them together and removing unused should also free alot of the memory. Some peope really like reorganizing memory, I consider kind of risky. Keeping backups of songs instead of high udos and backups for the glued audio files, etc is another good practice for this problem.
Come to think of it, I have run into this one. Last I had it was while chopping away at bass takes, creating stacks of cuts fades regions, etc. If you let it continue it just starts making things up, region placement, bad fades, anchor voodoo, just little problems like that which don't matter (!?!-JK). Cleaning house, saving all audio files as SDII or AIFF (whichever the existing ones are not), renaming regions were what I had done to overcome the problem long enough to get everything into another session. The memory situation is IMO a huge limitation in Logic, it really restricts what a user can do and requires us to put on the janitor jumpsuit way too frequently : (
7.1.1 was also a bad move for me, some people get along with it fine but it just caused more problems than any other version of 7 on my system.
I would guess this is a Logic issue and not an audio file or system issue and these are the things I do to overcome this problem and related ones. In fact, it is very unlikely IIME that it is anything nut a Logic issue. Good luck and if you see this one start moving things to a new session ASAP.