[WIN32SS?/EXPLORER?] Menu-placement is wrong after closing explorer

reported against 0.4.15-dev-8271-g61cdd02
This is the last menu-placement-difference to 2k3sp2 that I am currently aware of.

Reproduction steps

• open explorer filebrowser by double-clicking on my computer
• close the explorer window again
• move the mouse over an arbitrary position on the desktop
• now press the context-menu-button on the keyboard (next to the right AltGr) to open the desktop context menu

Expected result
the conext menu should be allowed to be opened here yet. That should require a mouse-click first somewhere on the desktop, and then the context-menu should be placed in the top left corner of the desktop (this is what WinXP / Win2k3sp2 do)

Observed result
the context menu of the desktop can be opened immediately and will erroneously be placed over the "My computer" icon (because we double-clicked there earlier to open the explorer window, and that selection remains active)
0.4.15-dev-8271-g61cdd02.webm
0.4.15-dev-8271-g61cdd02.log (is useless)

Notice: that if I would have done a single-click with the left mouse-button somewhere on the desktop before opening the context-menu with the keyboard-button, then the context-menu would have been placed correctly topmost-leftmost.

This bug/difference has absolutely no relevance for my usage of ReactOS in practice, I filed it just, because it is a difference to what Windows does. Super-low-prio.