Possible bug or change in 5.1.3 filename string handling?

I have a test case written in 5.0.1 that is working fine.  When I try and run the same testcase in 5.1.3 it fails.  I've narrowed the issue down to this:

 <s:Body>
  ${=new File("C:\\SOAPRESULTS\\requests\\" + (context.get('fileList')).last()).text}
   </s:Body>

Which I use to insert a file which contains the SOAP body (there is a Groovy script before this that prepares the fileList based on a directory structure). 

This works perfectly in 5.0.1.

In 5.1.3 I get an error response that the SOAP message had no body.  I noticed right away that in 5.1.3 the 'r' in the word requests from above was missing so added it in to no avail.  Went back to 5.0.1 and there was a double 'r' there now.  Something changed in the handling of strings in this version.

Thanks

Norm