Sounds like less of a bug to me, just like a car odometer can't be reset. There's a Trip odometer as well which indeed can be reset. Of course the "Odometer" is then just a meaningless number and I'm not sure why it's even implemented in the first place.
My eTrex-30 v2.80 resets Total ascent on a trip computer reset. Not saying that mussolini is lying though, the firmware in these units show a lot of funny/inconsistent behaviour...
Yes..the total ascent reset works on the Etrex 30 but not on the 20 when doing a trip computer reset.
The fact that the total ascent cannot be displayed as one of the fields on the trip computer but can only be displayed as a field on the map page may have something to do with it...