Does anyone have any kind of information about this issue ? Is this the right place to post about it ?
After several more tests, we are now highly confident that this is a driver issue. We have tested several AMD cards of different generations, with the respective latest drivers, and every single one shows this issue. The respective Piglit tests (sample-alpha-to-one tests) all consistently fail. Nvidia cards are not affected.
This is a problem for us. We're using the feature in a deferred image based LOD system. While we have a partial workaround, it is neither free (requiring an additional GBuffer pass), nor is it fully effective. The results are noticeable image quality differences between AMD and NV cards, which is hard to explain to our customers. I'm also having a hard time understanding how a GL core feature can be broken for so long. Surely it must have been flagged during AMDs internal QA / compliance testing ?
Any information would be highly appreciated.