I r stoopid - I thought I had a Sovereign elsewhere in the sockets in anticipation of the meta requirement (“META” should have tripped something, but it was 1am), but did not.
Please delete.
Are you activating and deactivating an equipped meta gem? I can’t seem to replicate this. For reference, there are +32 stam metas which would yield +35 stam if you have +10% from talents.
An additional note is that the +32 stam / 2% armor contribution meta calls for 1 red gem.