LibreCAD 2.1.3 leaves the taskbar visible when pressing F11 to switch into fullscreen

LibreCAD 2.1.3 from rapps
ros 0.4.12-RC-44-gca0e00e gcc dbg lin is affected
VBox4.3.12 + VBEMP + desktop resolution 800x600 32bpp

Expected result
The taskbar gets invisible when pressing F11 to switch into fullscreen

Observed result
The taskbar stays visible erroneously when pressing F11 to switch into fullscreen
0.4.12-RC-44-gca0e00e__LCAD2_1_3_affected.webm

Nothing is logged whenever I press F11.
The issue is old, I noticed it the first time when testing 0.4.10RC29.
I guess the issue is caused by a bug in our explorer_new.
I did not check, but would expect explorer_old and explorer of 2k3sp2 to not show the bug.