While holding a click with one mouse button and simultaneously clicking with another mouse button will result in that the second mouse click never gets through.
Steps to reproduce the behavior:
1. Connect using Web Access
2. Monitor mouse events using 'xev' in a terminal inside the session
3. Press the left mouse button but don't release it
4. Click with the right mouse button
5. Release the left mouse button
6. Observe that the right click never gets sent to the session
Found the problem with ThinLinc build 6262 in Chrome 77 on Fedora 30. Verified that the problem doesn't exist in Firefox 69.
Also tested ThinLinc 4.10.1 and saw that the problem was even worse before - using the same steps as above additionally the left mouse button 'up'-event never got through. This caused the left mouse button to get hanged with 4.10.1, both on Firefox and Chrome.
The remaining problem with build 6262 is likely related to our SetCapture() emulation, seeing as it isn't used on Firefox.
Edge (pre-Chromium) seems to also have bugs here. We never get a mousedown for the first press of the right mouse button in the above scenario. We get a mouseup after releasing it though, and after that we can get a mousedown. Very strange.
Let's test this with the new Edge.
I can verify that this is still an issue with new Edge and Chrome, but not Firefox.
Tested ThinLinc server 4.13.0post (build 2350) and webaccess in the following browsers on Windows 10:
* Microsoft Edge Version 95.0.1020.5
* Google Chrome Version 96.0.4664.45
* Firefox 94.0.1