https://github.com/tmk/tmk_keyboard/issues/265
With pressing Shift and '1' key you get 1 while with just '1' key you get !.
Keymap code on Alps64
15fe63e8d1/keyboard/alps64/keymap_pure.c
and guide.
77ac0805ad/keyboard/alps64/Guide.md
Consider the following scenario:
Shift was actually never released and is still considered pressed.
If such situation bothers you add this to your config.h
:
#define PREVENT_STUCK_MODIFIERS
This option uses 5 bytes of memory per every 8 keys on the keyboard rounded up (5 bits per key). For example on Planck (48 keys) it uses (48/8)*5 = 30 bytes.