System Information
Operating system: Darwin-19.6.0-x86_64-i386-64bit 64 Bits
Graphics card: AMD Radeon Pro 5700 XT OpenGL Engine ATI Technologies Inc. 4.1 ATI-3.10.18

Blender Version
Broken: version: 2.91.0, branch: master, commit date: 2020-11-25 08:34, hash: rB0f45cab862b8
Worked: (newest version of Blender that worked as expected)

Short description of error
Custom key-binds using "Key Modifier - regular key pressed as a modifier" are sending the single event trigger as well as the modified event trigger.

Exact steps for others to reproduce the error:

Setting the key map item:

• Open Blender preferences
• Add a new key map item (for this example, identifier: wm.search_menu)
• Leave the default "A"
• Change from "Press" to "Release"
• Click "Key Modifier" and press a regular keyboard key (for this example: F19)

Executing the shortcut

• In the 3D viewport press F19-A

Result

• wm.search_menu is triggered - search menu pops up.
• object.select_all is ALSO triggered - all object in viewport are selected.

Expected result

• Only wm.search_menu is triggered - Only the search menu pops up.
• Key-binds that use the unmodified key press should not trigger.