This is on the latest tip (c497f4b1). Just open any pattern, use Ctrl-T to open the variables table. Then press escape. Now you cannot open the Variables Table anymore. If you close the dialog with Alt-F4, it works fine.
Ubuntu 18.04, Qt 5.9.
It also happens for me with the AppImage I downloaded the other day:
DEBUG:Build revision: Git:c403baf205f0 DEBUG:"Based on Qt 5.13.2 (GCC 7.5.0, 64 bit)" DEBUG:Built on Aug 3 2020 at 00:37:47
No log messages. It displays “Showing variables” when it works, but nothing when it doesn’t work.
A quick Google tells by pressing Escape triggers the “reject()” call. In many other dialogs it does something with this, but dialogincrements doesn’t. Maybe related?