NitrokeyPro HOTP keyboard shortcuts stop working after app is opened

App Version: 1.3.1
Model: NitrokeyPro
Firmware: 0.7
OS: Opensuse Tumbleweed / Fedora 29

When the Nitrokey is connected to the USB port the double NumLock shortcut for HOTP generation works as expected.
Once the Nitrokey app is opened the shortcuts stop working and the codes can only be generated via the menu.

The only workaround I found is closing the app completely and reinserting the key.