Blank subject rule not working

Hello,

I have created a Transport rule on Exchange 2010 for emails with a blank subject. my rule looks like this....

When any of the recipients in the to field is 'Test@test.co.uk'

and when the subject field contains '^$'

prepend message subject with 'New Starter'

and copy the message to 'anothertest@test.co.uk'

When I have tested this anothertest@test.co.uk receives the email but with the blank subject. Every page and forum I have been on says that the ^$ is the prefix for 'Blank Subject' but this is does not seem to be working for me.

Any help would be very much appreciated.