I think the moral of the story here is that the computer is not good at
ad-libbing procedures.

I concur, but I think that's only part of the problem. A computer
won't ever get good at ad-libbing anything - that's a peculiarly human
trait. However, GOOD software allows the pilot to take control and
ad-lib easily and intuitively. I have yet to see any good software on
an IFR GPS.

The instruction you were given was clearly improper, but that happens.
Good software would be set up to allow you to easily deal with it,
rather than pretending it doesn't happen.

There used to be a similar quirk on the 430/530 when flying GPS
approaches with a hold in lieu (KEYQ is an example) rather than a
standard T. If you were approaching the IAF from some reasonable
angle, the controller would ask you to proceed straight in (no hold at
the IAF) but the software had no provisions for this, since it wasn't a
legal clearance. Thus it would not autosequence.

Garmin has solved the problem, and the solution is in itself an
admission that real life does not match the book. When you select the
approach, you are now asked if you want to hold at the IAF.

So it goes.

Michael