A drawing glitch in SumatraPdf 3.1.2 when restoring the window from maximized state

The Sumatra Pdf 3.1.2 from rapps.
The app renders its window properly when it is in maximized state.
But if we "restore" the window by double-clicking its titlebar, to transform it from maximized-state into "windowed-state"

exactly then it does not longer draw a static controls caption, with the word "Suche"/"search".

This looks like us missing a redraw.
If I drag the window afterwards, the control gets properly painted.
0.4.15-dev-1798-g6f2b94c_Sumatra.webm

0.4.15-dev-1798-g6f2b94c_Sumatra.log
the log shows not much of interest, each time I do double-click the titlebar to move from maximized into windowed-state ros does log:

(dll/win32/kernel32/client/version.c:140) VerifyVersionInfo -- Version mismatch(6.-1.-1:-1)

nothing more.