Hotkey wont work if its modifier is also being used as part of the trigger

This issue seems to only occur in this one program.

I have the hotkey Shift+a set in this programs hotkey editor dialog, I want to trigger it in AHK using Rshift and w;

RShift & w::
SendInput, +{a}
Return

For the life of me, it will not work. I press Rshift and w and nothing happens at all. Triggering the hotkey manually by pressing shift and a works just fine. The strange thing is the following works:

LCtrl & w::
SendInput, +{a}
Return

So does this:

w::
SendInput, +{a}
Return

I also tried to send Rshift back up before triggering the hotkey, no luck:

RShift & w::
SendInput, {RShift up}
SendInput, +{a}
Return

Is there a rule that says you cant use the same modifier as the target hotkey in the trigger that I missed? please dont suggest that I use other modifier keys, shift +[key] is all that I have left.

Any help would be greatly appreciated!

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