SMPlayer 18.5.0 erroneously leaves the taskbar visible when switching to fullscreen via button f

Install SMPlayer 18.5.0 from rapps
VBox4.3.40, VBEMP, 800x600 32bpp desktop resolution
and start up the app
When pressing F on the keyboard the app switches to fullscreen, it is not necessary to have a video running to retest this

Expected result
explorers taskbar should be hidden then, like 2K3_SP2_eng_ok.png

Observed result
explorers taskbar remains visible erroneously
0.4.12-RC-50-geb1a43d_SmPlayer.png
0.4.12-RC-50-geb1a43d_SmPlayer.log is quite uninteresting as nothing is logged at the moment of switching to fullscreen.

The first time I noticed this bug for this application was the rls test of ros 0.4.3. It happened for every release since then. Nothing new.
I could imagine the bug being in our explorer_new.