Well, I just downloaded and installed PDCU 4.40 on my Win 7 (64) PC, and I am pleased (and surprised) to say that 16 bit TIFF exports seem to work fine now.
I opened 3 recent K-5 DNG's through PDCU, did a few tweaks (mainly the optical corrections associated with using the 18-135), did a File > Save As > TIFF (16 bit) into a new export destination folder, and bingo, no crashes, no problems with all three DNG exports..
Before, PDCU would totally crash on 16 bit TIFF exports - ie the whole program would just disappear. Maybe the recent batch of .Net security updates MS released cured a problem or dependency somewhere.
So for me, the problem does appear crushed now.