Attempt close the modal dialog after merging a branch leaves application in unresponsive state

The application stays in an unresponsive state after pressing Return in the Merge Progress Dialog:
1. start a merge by right clicking on a branch tag
2. confirm to do the merge
=> the merge progress dialog (log output enabled) shows up with the single "close" button
3. quickly press return (it is unclear whether the return has to happen before the merge has finished or not, but it seems this does not matter as this issue happens 95%)
=> the application freezes in the following way:

• the modal dialog stays open and receives input (pressing return again makes it flash)
• since the dialog is modal, you cannot do anything else and have to force close using Alt-Cmd-Escape.

When you confirm the close dialog using the mouse instead of pressing return, the issue does not occur.

Since I'm a keyboard power use as most developers this issue is really annoying.