Shift modifier not working in macro

Have a strange issue - using this macro:

#showtooltip
/cast [mod:shift,@cursor] Tar Trap; [@cursor] Freezing Trap

The key-bind I use for this macro is NUM 3.
It will cast Freezing Trap, but will not cast Tar Trap.
If I change the modifier to ‘ctrl’ it works fine.
If I bind shift-NUM 3 (page down) to a slot on the action bar it will work to cast whatever is in that slot.
Page down is not bound to anything in as far as I can tell - I removed it from it’s original keybind.

Shift-Num3 = Page Down

The only Num keys that work with shift are 5 / * - +