Fortunately its one of those things that is an annoyance and does not happen all the time. Usually just recreating the curve and rebuilding fixes it.

Just a heads up, sometimes rebuilding manually is the ONLY fix so don't get to wrapped around the axle fighting it.

It's definitely an internal thing because the only way I know to ALWAYS fix this kind of problem was to export in a format the Autodesk in their infinite stupidity took out of Maya so now you cannot fix it PERIOD without just starting over and building the patch manually from scratch (sigh).

I forget what the export format was but when autoedesk took over Maya they removed it. If you find some old Gnomon nurbs modeling tutorials it's one of the first things they show you - the problem and then the fix export and re-import the model in the magic format and poof the curves rebuild properly.

I guess since nurbs have fallen out of favor that no one at autodesk or alias before them felt it was worth putting any effort in to fix.