After loading sources, I'm at 135M.
After loading a character, it jumps up +15-20M and never goes lower. Hit a "reload sources" and it jumped up to 210M. Even a GC never takes it lower than 200M. I then reload another character that uses different sources, and it's now 360M (GC drops it to 210M). Another reload of a different character takes it to 300M, which doesn't lower with GC. Unloading all characters and source materials still never goes below 270M at this point. It seems the more times I load sources and characters, the higher the minimum goes.
The leak is caused by CharacterFacadeImpl instances not being released. While they don't take up a lot of memory themselves they do refer back to the datasets which can be quite large (20Mb for a simple one, 60+Mb for large combined sets). This mainly has a visible impact when you are changing sources frequently.
Due to the intrusive nature of the changes required to fix this I'm putting it on hold until post 6.0.