Viewing a women-specific race, I expect that D is locked due to my recent upgrade, but the UI is also showing the restriction icon for Pen B.
When I click on B, it still seems to enroll me (the background switches from orange to green and I show up in the list), but the restriction badge remains on top. I’ve seen this on a few race event pages, so filing the bug now since it doesn’t appear to be a one off.