This is connected with the recent change that prevents observations from becoming RG if the observation taxon and the community taxon are not the same. The previous system had meant that the DQA could make observations RG with only a single species level ID (observation taxon) that was treated for all practical purposes as though it were the community taxon.
The “solution” was to make observations casual if the DQA was applied in such cases. To prevent observations from unnecessarily becoming casual, the DQA button was subsequently disabled for observations when the community taxon and observation taxon are not the same.
Note that this only applies at the point in time the DQA button is clicked: it is still possible for users to add a more specific ID on observations where the DQA has already been used. In such a case, the DQA is not erased (because the community ID has not changed), and the observation becomes casual.