This is weird but it's not a bug.
I still don't understand why but somehow the compilation process grabbed my old copy of RegExpr even though I had excluded it from my package and dumped it into the x64 folder for the project. Then somehow, and I stil don't know why, the compiler decided to recompile part of SynEdit even though I'm not using it (but then maybe the gui for the Test framework uses it?).
What's odd is that I did several compile clean but the cleaning process did not delete the offending .ppo file from the directory. Once I took it out manually, the program recompiled just fine.
So, yeah, it's a solution without comprehension... but I'll take it over being stuck.