Blueprint uncompiles when restarting editor

I have a game where most of HUD is made using blueprints, but three of widgets won’t work normally for unknown reasons.
I’ve just started the editor, it’s fresh and clean, and immediately ran play-in-editor. The gun is depends on what HUD chooses and if nothing was selected the gun will shoot as defaults saying. Usually if there at least anything in HUD gun will choose defaults from HUD and shoot differently.
When game starts Game Instance loads up all presets for gun from specific folder and sends them to HUD to display, so I thought that the only reason for gun to “shoot it’s defaults” is if there will be nothing loaded from folder. Apparently not. When I opened up library I saw this:

These small buttons are in their default state, but Game Instance actually sent data (that I call setups).
I also should mention that editor gave me no warnings.
So when I’ve tried to launch PIE again editor now said that for these three types of widget there is an compilation errors. I checked an errors, all about the same function, but still doesn’t makes sense:

This function does exists in LibraryWidget, but for some reason it wasn’t hooked up. Of course if I just recompile then everything’s fine, but this is really annoying to recompile each time I need to restart the editor, especially if I’am still not so good programmer and my code crashes the editor pretty often.
What is wrong with blueprints?

This problem is gone in UE 4.12. Looks like it was a bug.