That is a bit of an odd one. Did you try doing a fully clean driver install again for the card? Maybe something happened during driver installation that is keeping the software from consistently communicating properly with the card. I personally don't use Precision anymore because I had many system instability issues with that software running on my particular system(s), but your mileage may vary. it could also have something to do with the version of the software you are using not playing nice with the card in general. If Precision v.2 works for your card then I would stick with that and go from there if it will allow proper voltage changes.
Also, be sure to update your profile here with all of your system specs, there might be some information there that could help us out a bit more!