${ThreadIndex} removed from DataSource | File option when SOAPUI re-opened

For our Thread Strategy load testing we created text files with unique data for each thread. Each file has a unique integer appended to its name, and each thread finds its corresponding file from a Data Source test step, with 'File' set to: 'loadtestdata/testdata${ThreadIndex}.txt.' Upon closing and re-opening SOAPUI, the Data Source 'File' option has reverted to loadtestdata/testdata.txt So, we must re-edit this option every time we re-open SOAPUI.

We are using SoapUI Pro 2.5:

Build dist-76-2008-11-21, Build Date 2008/11/21 12:00