No, it is working as it should.

The Pgshortc.txt file says that if you enter Csus2, it will be converted to C2. The file explains that this is a built-in shortcut. You cannot change it; it just works.

By the way, if you do create a shortcut for some other chord type, don't use any pitch like C. You want the shortcut to work for all pitches.

Here is an example of one line in my shortcut.txt file:
a@7alt

So if I type a chord of Fa then BIAB creates F7alt

BIAB 2025 Win Audiophile. Software: Studio One 7 Pro, Swam horns, Acoustica-7, Notion 6, Song Master Pro, Win 11 Home. Hardware: Intel i9, 32 Gb; Roland Integra-7, Presonus 192 & Faderport 8, Royer 121, Adam Sub8 & Neumann 120 monitors.