Yes I have tested it, and I was not aware of bug 51140 when making this patch. I was working on fixing an issue in a game called [ISLAND](https://github.com/ValveSoftware/Proton/issues/452) in proton. I tested the game on Windows 10, and with message spy++ I could see that indeed WM_ERASEBKGDN was sending when ending the video. Here is the relavant logs from spy++, it was sending WM_PAINT during the video and when I clicked stop it sent WM_SHOWWINDOW
``` <004863> 0014041A P WM_PAINT hdc:00000000 <004864> 0014041A P WM_PAINT hdc:00000000 <004865> 0014041A P WM_PAINT hdc:00000000 <004866> 0014041A P WM_PAINT hdc:00000000 <004867> 0014041A S WM_SHOWWINDOW fShow:False fuStatus:0 (ShowWindow was called) <004868> 0014041A R WM_SHOWWINDOW <004869> 0014041A S WM_WINDOWPOSCHANGING lpwp:15E9FEAC <004870> 0014041A R WM_WINDOWPOSCHANGING <004871> 00170F76 P WM_PAINT hdc:00000000 <004872> 0014041A S WM_WINDOWPOSCHANGED lpwp:15E9FEAC <004873> 00170F76 S WM_ERASEBKGND hdc:29012B2D <004874> 0014041A R WM_WINDOWPOSCHANGED <004875> 00170F76 R WM_ERASEBKGND fErased:False ``` Here you can see the position is clearly changing and both WM_PAINT and WM_ERASEBKGND is being sent
This is very similar to my logs when ending the window in wine [log](https://gist.github.com/CKolle/2b44d8a0f8626cecd3e591d8f8597857) but here I get a deadlock.
Leading me to conclude that VideoWindow_put_Visible most likely doesn't hold the lock when doing the ShowWindow.
Quick note, I had to enable "Aditonal Windows -> All WIndows in System" to see the WM_SHOWWINDOW in spy++. Also in my wine log there is some TRACE for when I was debugging.