All I can figure is that the threadbit template for 4.1.x is slightly different than that for 4.2.x, and the str_replace() function I use to modify the templates isn't working as planned. :)

I got this to work with the manual template edit to the threadbit template, disabled Modify Templates For New Phrase, Username Markup In Threadbit (forumdisplay) and Username Markup In Threadbit (Last Post By) from the plugins and activated Username Markup In Threadbit (search_results) and Username Markup In Threadbit (threadbit) from the manual plugins created ....maybe this will help out ...