Professional :: After Saving, Closeing, And Reopening .fla Files, Assets Are Missing From Timelines?

Well ok so, I've been looking, and I see similar things, but not really going anywhere. And I also can't make it happen at will, it just happens.But often enough to make it really frustratrating and scary to close a file.It's easy to explain what happens when it happens.I open a file, work on it for a while, during which time I've imported some images or wav files and placed them on the main timeline or movie clip timelines.I can test and save the file often while I'm working and everything seems fine.  Eventually I close the file.When I reopen the file, the imported images are all missing from the timelines. It's very odd.All of the edits are still complete.The keyframes where the assets were placed are still where they belong, and the assets are all in the library.So I have to go through to each location and put the image or wav file back in its keyframe where it belongs.So far, it seems like after I go through this exercise once, it doesn't happen again.Here are the only details I can really offer.
 
Don't know about new files.The files I'm working on originated on a Mac, and they may have gone back and forth between CS4 anc CS5 versions, and finally are going to CS5.5 on a pc.I have seen this problem now in both CS4 and CS5 on both the Mac and the pc.It only seems to affect newly imported assets.Doesn't seem to matter how they're imported.Sometimes I use the menus, sometimes I drag and drop them into the library, sometimes I copy them from other Flash files and paste them into the current one.So far, I'm not sure that his problem has been seen on my own equipment.Just at my contractor location.Because of the things I'm seeing around, I'm beginning to suspect that this could have something to do with these RAID systems these guys usually set up, which I know virtually nothing about. RAID5 on these new machines.But I'm wondering if some caching of something is going on somewhere, and somehow not being saved somewhere else

I'll probably start trying some things like importing assets, saving,closing and re-opening before I do anything, or some such exercises, in an attempt to make it stop happening.Like I said though, it's virtually impossible for me to reproduce.It really seems to be one of those things that just likes to happen out of the blue.Maybe 15 to 20 percent of the time.Probably whenever it'll do the most damage.