Well, two steps forward, one step back: We verified that the request succeeds on 0.92 … but later the same request failed on the same server. There were no configuration changes between when requests succeeded and when they failed.
This still only seems to be an issue for creating Observations of concepts of boolean data type. We will test all data types just to make sure that it is only boolean ones that throw this error.
One suggested workaround is to use coded concepts with answers of “True” and “False” instead of using boolean concepts.