Hey ,
I tested this in 4.5 and didn’t encounter problem. I started a new project (Third Person BP template), opened MyCharacter Blueprint, and used Task Manager > End Task on engine. When I reopened project and chose to recover assets, BP opened as expected.
Are you in 4.5 or an earlier version of engine? You mention Force Quit… are you using a Mac? Does this happen in a new project or only your current project? And does it happen consistently? Thanks!