Strange behavior, not sure if intended
So someone on my server complained that filter behavior wasn't working correctly, so I had to investigate the matter. It seems to me, from the mod description, that the filter behavior was intended to work for all users. For whatever reason, in the ChangeBuildingGrade() function, around line 328 or 329, it makes an odd test:

var allowed = player.IsAdmin;
all_blocks.RemoveWhere(b => prefabs != null && (!allowed || filter && !prefabs.Contains(b.prefabID)));​

This seems to imply that the filter is meant only for admin users. Well, more than imply, non-admins get EVERYTHING removed from their upgrade list. It says "Finished Upgrading" and doesn't actually attempt to upgrade anything because the !allowed test removes everything from the list. 

I've already removed the test myself, it seems like that filter line should probably be dedicated to actually filtering for the correct block type. Any other types of filtering probably belong earlier, and if admin is the test, it's going to be true or false WAY before the RemoveWhere() line. That test should probably execute only once, as early as possible, and not do the rest of the stuff, IF it is the case that only admins get to filter. 
my server has just started to see this bug aswell and i have to remove the mod off the server till there is a update