There was a bug report posted on RNAAS
https://github.com/David-Sweeney/Astroquery-Gaia-bug
I believe it's a duplicate of #2421, which we decided was not an astroquery bug but instead a bug (or feature) of the Gaia database.
Given that at least some users are so surprised by this they write it up formally, it might be a good idea for this to be explicitly documented.
I'm just cross-posting here because I don't see any record of this bug being reported as an issue.