Two seemingly identical tap-hold-press one-shot layer-held config lines acting differently

[brandonbeaumia]

I was able to set up a key that is "tap for one shot layer, hold for a different layer." The line looks like this and behaves as I would expect:
spnmsm (tap-hold-press 0 $ht (one-shot-release 500 (layer-while-held spaces)) (layer-while-held numsym))

Following that pattern, I would like a "tap for one shot layer, hold for control", but this practically-identical line isn't working:
splctl (tap-hold-press 0 $ht (one-shot-release 500 (layer-while-held spaces)) lctl)

The config parses fine. The hold-for-control part seems to be working fine, but tapping never activates the OSL despite the same settings as the line that works correctly. I must be missing something pretty obvious, can anyone tell what's wrong here?

[gerhard-h]

have you tried binding splctl to a different key, does it work then?

[brandonbeaumia]

Oh my. It did, and now I just figured out why thanks to your help. This whole time (as in, months) I had been under the assumption that my programmable keyboard has been sending left alt with that key in order to match my laptop keyboard layout, but I had it set to left control. Kanata never saw a left alt keycode to convert to my intended function, and that's why the "control" part of holding the key seemed to work! Just fixed my keyboard layout, thank you so much.