bounceback into variadic block does unexpected thing

[brianharvey]

Make this block:

(I was looking for an example of something that throws an error message.) Now drag out the MY block and drop it someplace that won't accept it, such as the sprite corral background. It visibly bounces back into the ASK block, but not to where it came from:

It should really remember exactly where it came from until successfully dropped somewhere else. (Actually, it turns out that pushing Undo after a successful drop has the same problem, sometimes, depending on just where you dropped it. so I guess even after a succcessful drop.)