I have some RAM code that takes up 478 bytes, and I'm storing it at $8000.  If I run an application, is there anything from $8000 on that needs to be preserved? 

I'm asking because it seems like exiting the app with JForceCmdNoChar might be causing problems.  It could be another reason, but I don't know.

Hmm, the first 256 bytes I've never had a problem with using, but the 119 bytes immediately following is called "ramcode". I believe I have seen the OS back up data there when calling a bcall and when copying code that needs to access off-page calls (such as for working with the archive). That might be causing the problem

EDIT: Hopefully somebody who actually knows will come along. Have you tried stepping through the code? Maybe create some code that just edits that area of RAM and tries to exit, see if that causes problems.

I'm going to guess you haven't seen this yet.

Anyways, at 478 you shouldn't have to worry about anything. However, if you go past 560 on specifically the 83+, you'll have to use bcall(_fillBasePageTable) when you quit.

Indeed, all of that space (up to 822Fh) is used as scratch space by the OS; there's nothing wrong with using it for your own temporary storage.  But as Xeda says, many system routines will use ramCode themselves, and could be overwriting your data.