haroopad doesn't reopen after being closed on Windows 7

After being closed with alt-F4 Haroopad doesn't reopen again. The process starts (I can see it in task manager) but the GUI doesn't show up.
I also tried killing the process or the process tree via task manager and then reopening the program but still nothing: the process starts but not GUI.

I use windows 7, version 0.13 of Haroopad.