I've /never/ had problems with any of my domains with these servers.
Guess you have more good karma in the universe than I do :)
Are we still just talking about delegation changes? Because I can
think of numerous DNS related 'tales or woe' from telcos, but they tend
to come back to general competence issues and corporate lack of clue.
I have always found it works quite well (but is irritatingly time
consuming) to get the telco, or whoever the other party is, to change
their zones to return the new addresses we want to have returned after
the move, then transfer the name to our name servers (with no changes
in the zone). Then the telco can take their sweet time with the
removal of the name. Although we recently go bitten (see last post)
with a telco who still thought they were primary several years after
the name was moved.
We are fairly small too though, and not everyone will have the time or
patience (read 'budget') to be as risk adverse as we are. Having said
that I ran Joe Abley's 'stalezone.sh' and have a pile of work to do too
:^/