I've got a really dumb UI made from qt4-designer, pythonized with pyuic4, and an app that imports and creates the ui. Inside this app I make a qtgui.time_sink_c and a qtgui.freq_sink_c. My UI has empty frames that I place a sip-wrapped instance of the qtgui widgets in.
On one machine, let's call it pepper (running i3), the qtgui widgets load up and the whole things displays/behaves nicely. On another machine, let's call it saffron (running KDE), the UI shows up blank and I can't exit (have to kill it from terminal).
Both machines have GNU Radio v22.214.171.124 on Debian 8.3 with the only major software difference being KDE vs i3.
As a sanity check I use a third machine (let's not call it anything special) also running Debian 8.3 and KDE which has the same issue as saffron (no widgets displayed). Switching to gnome shows the same behavior. Switching to i3 works (all widgets show up and qtgui widgets are displayed). If I never create the qtgui widgets in KDE/Gnome then the other widgets will show up. If I create the qtgui widgets, but don't do anything with the I have the same issue (no other widgets show up)