The "GeForce" line of Nvidia cards is NOT supported at ALL by Maya, per the Hardware guide on Alias' site.
(only the "Quatro" line is qualified).
Alias knows about the viewport refresh issue, and has documented it online, along with some extreme cases of system instability using the GeForce line as well.
HOWEVER, I have a brand new Nvidia FX 5700
Ultra that I got yesterday for my brand new Maya box that I am testing tonight, and I'll let you know if that still happens with my particular drivers.
(I'll post the version # if all is fine when I get home)
If it does happen, I'll post a workaround that I have found is a LOT easier that touching the timeline
Israel "Izzy" Long
Motion and Title Design for Broadcast-Film-DS