Copy Sequences from Project to Project in Productions

A lot of the premiere projects I work on are actually productions. We usually have a master project, an editor project, and a delivery project. This helps us keep things separated, but I've run into a problem. For some reason, I can't copy or drag sequences from project to project in a production, even if I have read/write access to both of them. I swear I've done this before, but it seems to not work anymore. Does anyone have any suggestions?