As the title says, if you force a robot to place the wrong pipe, with a ghost for example, it places it without any problems and everything works fine.

It's a vanilla bug! I can't believe you're the first person to have found that. Looks like I may have to make a forum account and file some reports.

Are there any pipes with material constraints in vanilla? Maybe that's why no one has found it :D

Nope, it happens even when the pipes are filled with different fluids in them.

now my existence has a meaning :D

Good thing I did some searching before I go wasting people's time, here's an old thread and another.

Bad luck for you, I'm afraid.

You like to destroy other people's dreams! Well done!