Just guessing but I suspect this issue is related to the way the data “collection” for that grid is populated. i.e. a bug, not under your control… will need to rely on Epicor to fix in a future version.
If so, this may be a possible workaround in the meantime:
When you inactivate an Indirect Code, append a prefix to the description too… … e.g. zzz
Giving users a visual cue that it shouldn’t be used anymore and (assuming it is being sorted by description) it should end up at the bottom of the combo listing.
I have used the “zzz” prefix trick on all kinds of codes in Epicor.