Not sure it’s just r134 this happens in, I’ve often had the place item menu close during prior versions when placing several objects (just… didn’t think about making a bug report yet I guess ).
Edit: For some reason this post has appeared above @Didis’ post directly below . Anyway, it’s a response to that one, WRT the place items UI closing itself.
The menu sometimes closes by himself. It’s not hard to reproduce. When you place an object and after place another object the menu closes and during this step at a moment, the menu will refresh and the next object you will place will close the menu.