Regular expression inside Save Arrachments Activity

Please help me understand.
I have an regular expression
^(some text)( )((0|1)\d{1})-((0|1|2|3)\d{1})-((19|20)\d{2}).(xlsx|xls)
If use it with isMatch activity it works fine, I get true when expected.
But when i tried to apply the regex inside SaveMailAttachents->Filter
it doesn’t work. As I understand, for all files “False” returns and I do not save any files.
Why the regular expression does not work here?
Thank you