This might be a "Qt being like GTK" issue, but I notice that QLC+ for me looks like GTK, but Ctrl-PageUp/Down don't switch tabs, like they do in normal GTK programs.
Specifically this is awkward when setting up multiple fixtures in a scene; normally I'd expect Ctrl-PageDown to switch to the next tab in the ribbon set, i.e. the next feature, where I could type in more numbers. It seems that QLC+ or Qt is ignoring the Ctrl- modifier and treats it the same as a regular PageDown, which decrements the currently-selected fixture channel by 10.
Q Light Controller+
Official forums of the QLC+ project