Operating system: Windows 10 Enterprise (Version 1803)
Graphics card: GTX 1070
(2.80, 16fc62e15f0, blender2.8, 2018-12-12)
Short description of error
Blender will not send RELEASE key events to a running modal operators if an operator or dialogue is associated with the key.
Exact steps for others to reproduce the error
Starting form the Simple Modal Template script logging events shows missing events.
Pressing "Q" will generate a Event with type Q and value PRESS but releasing will not create an Event with type Q and value RELEASE.
Pressing "W" on the other hand generates both events
Pressing "G" will also only generate the initial PRESS event.
The attached .blend file contains a simple script that logs key (and mouse) events to the console to show the missing events.