I've checked both the references and the base items and don't see any flags that might cause this. Does anyone have any ideas? Thanks!
Check the http://cs.elderscrolls.com/index.php?title=Talk:ResetInterior
There is some info there that may help you.
This statement, in particular, may be the answer to you question:
"The slightly longer answer is: Food respawns. Other items don't. Haven't checked non-food ingredients. Scruggs 18:24, 16 October 2008"