I have a maestro view where I've created various corners. There are some views (notably older ones) where some corner setups do not show up in the corner drop down menu when in the Explorer view for the test. When I ascend up to the Assembler view the corners are present and the Explorer views can still somehow "see" them because they execute when a test is run from the Explorer view when they are not in the menu. It also creates a conflict if you try to generate a new corner within the Explorer view and says that the corner already exists.
Here is my corner menu from Assembler:
And here is what it looks like when I descend into one of my tests:
It doesn't seem to be related to newer views or even ones generated within different Explorer views as the last four corners shown were just generated in a different Explorer view.