I've noticed that the detour mechanism affects a particular construction that's used in a few places around here. I'm not sure where this would best go in the Wiki, or if this configuration is used elsewhere, but I do think it should be here to guide editors.
Any time a U turn segment splits off from a left turn lane, U turns are prohibited by detour prevention — because 2 segments are required to make the U turn, it's treated as a detour.
This configuration does not work:
The configuration on the left works, the configuration on the right does not:
This configuration works: