Haven't run into this before, but try setting the %CurrentPDFVersion% variable to c:\test\PartA_R2.pdf and use only that in the delete dialog and see if that works for you.
I'm testing something similar. I noticed there is a delay - I've seen it take a couple minutes for the file to disappear.
Below image shows the 3 variables I used, since nesting functions didn't seem to work. I used this to change extension to .pdf.
I also put in a message box that shows me the name of d_deletename so I know what it is trying to do, sounds like you have that already...
The problem I'm actually having is I need a wild card. I can't get it to work when there is an unknown date (inserted by pdf task) at the end of the filename (eg 42019 - Frame Holder Gear-02_06_2014.pdf).