Questions IN document not being released automatically

It used to be that we could setup specific purchase UOMs directly on items and define a conversion factor to a common UOM defined in the Units of Measure table and everything worked fine.

For several months now we've noticed that if these specific UOMs are not defined in the UOM table, when the distribution document gets released (eg. Purchase Receipt), the generated IN document doesn't get released - it stays in Balanced status. We have to add the UOM to the main UOM table which is really ugly as that UOM is only specific to a single inventory item. 

Has anyone else noticed this? I really hate cluttering the UOM table with all these specific units of measure but it seems we have no choice now.