Compound Macros not working

I've been running with my team quite nicely the last few months, and I came across a very strange problem. On my Shammy healer I have a macro that looks like this:
/cast [@party3pet,mod:shift,mod:ctrl] Chain Heal
/cast [@party3,mod:shift] Riptide;[@party3,mod:ctrl] Healing Wave; [@party3,nomod] Chain Heal

I then set this up to be triggered by F6... and it works a champ.

I create a similar macro on my low level priest:
/cast [@party3pet,mod:shift,mod:ctrl] Heal
/cast [@party3,mod:shift] Renew; [@party3,mod:ctrl] Heal; [@party3,nomod] Flash Heal

And it will not cast the heal on the party pet no matter what. I've gone into the Keybinding interface and ctrl-shift-F6 is NOT bound to anything. Just in case I bound it, then "unbound" it. The other portions of the macro work - just not the compound shift+ctrl. I then tried shift+alt and ctrl+alt ... but none of those work either. I checked the bindings.cache file - no binding are showing there for anything but F6 (which is bound to the macro key as it should be).

So - why is it that my shaman can use that macro but the priest cannot?

Or, I guess a better question: How do I imperically determine exactly what keybinds are in-use (if the keybind interface isn't telling me)?

Make sure that ctrl-f6 and shift-f6 isnt bound the only way to make sure 100% that they aren't bound is to bind them temporarily then clear the binding right afterward.

What also might helps is delete the macro and recreating it sometimes I macro slot gets funky for some reason.