Created attachment 196515 [details]
test case demonstrating bug
ARIA presentation role inheritance does not work with some elements when using some CSS properties like display:inline-block. See test case for more information and demos.
James, your test case works as expected for me at this point (TOT). If this is still an issue let me know.
Specifically, the second test group does NOT have an additional AXGroup around the AXRadioButton as you've mentioned. Which, DOES exist as expected in the last group.
Yes, this is working correctly at top of trunk.