invalid version slug message

Lower priority, not critical, there are many messages in the logs that match this pattern "Attempted to set invalid version slug: 1_81_0" which occur when successfully retrieving docs for 1_81_0.
https://www.stage.boost.org/doc/libs/1_81_0/libs/beast/doc/html/beast/quick_start/websocket_autobahn_testsuite.html
Not to suppress the warning, but rather determine what's happening, why it's happening, if something should be fixed.