bug#21621: Bug | grep | Running in loop

[Gino Atlas]

Dear ladies and gentlemen,

I would like to report a bug.
When I run this command:
grep -rl '^PATTERN$'.
^C
(Pay attention to the non-whitespace between pattern and target 
directory.)

It seems like it’s running in a loop, though, I was expecting a timeout 
would occur after a while.
Can you confirm it's a bug and the behaviour is expected?

Best Regards
Gino Atlas