ASt Trimming Problem

[ShazzleCov]

Hey everyone, been using nurbs for just over a year now and ive encountered a very odd problem and i cant think of why this is happening,

Im trimming the areas out for an alloy and as you can see three out of 5 trim fine but when i try to trim either of the other two, another surface appears out of nowhere =S

This seems to happen when dividing and discarding the surfaces.

can't quite figure out what im doing wrong or why it is doing this?
any suggestions?

[nfsc]

this happened to me once...but i cant remember what i did to fix it are you using revolve surfacing to make the initial surface? cause i think it was revolve or rail surface that gave me problem

[ShazzleCov]

oh no I found what it was its just the display settings, I just needed to turn the tollerance to 0.0010 and the tessalator to accurate, maybe that would help if you ever get the problem again?