It appears to be Debian’s stance that the behavior I experienced is completely normal
Unsurprisingly, I awoke to a disappointing response from the Debian bugs team. The email was sent privately so I wont post it here, but it boils down to “nah man, this is normal”. On a whim, I have therefore asked the Debian TC if they have a policy on quality and correctness review of patches inserted by Debian into upstream software: