Right now we generate duplicates in a few cases, e.g.
- type / members
- properties / getter+setter
It's not a big deal since the linker removes them, however it's extra metadata when the linker is not used (e.g. more common on the Mac side).
The duplicate should be removed (e.g. no need for a member to be marked as it's type). We should also have an introspection test to check for duplicates (no point in trying to do this manually).
The introspection tests have some dupe checks for availability in PR3141 
However they are presently disabled since there are thousands of cases being reported. The work on the generator needs to be done before re-enabling them.