Comment 4 for bug 1507421

If a dockable/docked dialog hangs, and inkscape as a whole appears to freeze (no buttons clickable anymore) - I'm observing similar issues with all dockable dialogs, possibly related to changing scrollable lists (here e.g. the one titled with 'Style') - try these steps:
1) move the input focus to the canvas (single click on the canvas)
2) zoom in/out (e.g. with keyboard shortcuts '+', '-').
That seems to help in such cases; AFAIU not related/limited to 'Text and Fonts' or an individual font (I initially came across this in the filter editor, as well as in the Glyphs dialog).