Non-greedy option greedy?

[SanskritFritz]

Hi there,
i execute this command in bash (cygwin):

echo CC-3623843-4/2008 | grep -P -o --regexp=-.*?/

and I get this result:

-3623843-4/

Shouldn it be

-4/

Thanks in advance for your help!
SanskritFritz