This is an oddity.

You can bind these for your hotbars :

Ctrl-Shift-1
Ctrl-Shift-2
Ctrl-Shift-3
Ctrl-Shift-4
Ctrl-Shift-5
Ctrl-Shift-6
Ctrl-Shift-7
Ctrl-Shift-8
Ctrl-Shift-9
Ctrl-Shift-(minus)
Ctrl-Shift-(equal)

You CANNOT bind :
Ctrl-Shift-0

Why?

Alt-Shift-0 works.
Ctrl-Alt-Shift-0 works.

So uhm, I'm guessing this is a bug?