COMBO layer mod keys

[dafzor]

I'm trying to have some keys act as normal modifiers when I have mod9 pressed (relevant config bellow).

# Make CapsLock key the virtual modifier MOD9 key. If you tap (press+release) CapsLock, nothing happens (No Operation).
REWIRE    CAPS   MOD9    NOP

# helper for easier mod + arrows
COMBO    A  [...& .... ....] > key (LCTRL)
COMBO    S  [...& .... ....] > key (LSHF)

# arrow navigation
COMBO    J  [...& .... ....] > key (LEFT)
COMBO    L  [...& .... ....] > key (RIGHT)
COMBO    I  [...& .... ....] > key (UP)
COMBO    K  [...& .... ....] > key (DOWN)

What I expected to happen when pressing the combos would be:

• MOD9 + J => Left
• MOD9 + A + J => Ctrl + Left
• MOD9 + A + C => Ctrl + C
• MOD9 + S + L => Shift + Right
• MOD9 + A + S + I => Ctrl + Shift + Up

However the Ctrl and Shift combos just seem to simulate a single press instead of mod key being held down which means they don't work as expected.

I couldn't find any help on the wiki on how to achieve this, has anyone done anything similar? is it even possible?