From the colour, it looks like you’ve drawn the dimension on B.Cu. You’re not supposed to do that anyway. I usually draw dimensions on User.Drawings. Then the text will always be correct whether you have or have not flipped the board view.
Clearly the consensus is that the software should lightly punish people for having the audacity to measure things on the flip side. I, for one, have nothing but respect for our new hand-slapping UI overlords. Thanks for your help!
It’s not punishing anybody for measuring on the flip side. Try exporting your board as gerbers - your measurement on that copper layer will be exported as if you wanted it preserved for ever on your PCB copper. That’s why it gets flipped - it is nonsensical to have non-inverted items on a rear copper layer.
Place the measurements on a non-copper, non-inverting layer (like the user layers suggested above) and they a) won’t turn in to copper in your gerbers, and b) won’t be flipped.