ui: letting go of shift while dragging a buffer makes the buffer disappear

[chrissexton]

When I drag a buffer from one spot to the next using shift+drag, it will disappear and become unretrievable if I accidentally let go of shift mid-drag.

A silly screencast attached:

[eaburns]

Is that consistent? The intended behavior (which is the behavior that I get) is that it gets put back from where you took it.

[chrissexton]

I was able to do it four or five times reliably after I verified how to reproduce it. Might be interesting to see if another Mac user has the issue.

[eaburns]

I marked it as "help wanted", because I don't have OSX.