GREP: Zero or more break characters (e.g. ~R*) doesn't work?

I'm trying to make a GREP rule that includes something to pick up any frame break characters at the start, if there are any, and carry on if there aren't.

This should do the job perfectly...

~R*.someGREP

...but it doesn't pick anything up. The .someGREP should happen whether there are break characters or not, but it does nothing. Other things I've tried with the same result:

~R?.someGREP

(~R?).someGREP

(~R)?.someGREP

(~R*).someGREP

(~R)*.someGREP

(~R|.).someGREP

...why are these not working? How can I tell it to pick up any frame breaks, if there are any, and carry on regardless if there aren't?

All of these with a regular character (e.g. 'R') instead of the break character (~R) work as expected.