Tiling not working when whiskermenu assigned to

Hello.

XFCE 4.20 Tiling with arrowkeys (not keypad) does not work, if whisker is assigned to the super-key.

Wanted behaviour:

<super>+<arrow-left> = tile window to left
<super>+<arrow-right> = tile window to right
and so forth for other tiling places like top or bottom.
<super> = xfce4-popup-whiskermenu 

IMHO this makes sense, because "super" is the "windows"-key and my brain is hard mapped to this behaviour ;-) until 4.18.

But, this combination does not work with xfce4 4.20

Steps to discover the issue (also tested on clean VM installation):

Assign shortcuts for tiling windows via "Settings Manager > Window Manager > Keyboard GUI"
/xfwm4/custom/<Super>Left                    tile_left_key
/xfwm4/custom/<Super>Right                   tile_right_key
Tiling works... till now. 
Assign xfce4-popup-whiskermenu to <super>
Tiling refuses to work.

Interesting, that "super"+"letter" works, nevertheless what whisker is assigned to. E.g. "super+t" can be used to open the terminal.

Please see also: https://forum.xfce.org/viewtopic.php?id=18838

Would be great if you could look at it Thanks!!!

Cheers! Jens

P.S.: Workarounds could include assigning Whisker to a different key (e.g., "super+a") or reviving XCAPE.