I’m experiencing strange behaviour when trying to use the measurement ruler. It works fine if no features are enabled but when turning on small caps, it stops measuring and displays the previous measurement values.
Version 2.6.5 (1342)
issue_measurement_smallcaps.mov.zip (2.6 MB)
What happens when you switch the feature from the popup in the lower left?
Same issue when using the lowerleft popup. It seems like it’s something specific with smcp. When I try the same with c2sc it works fine.
Because it works for me.
Trying it on another file and it works fine. 
Maybe there is a conflict with a plugin. If I find a way to repeat it, I’ll post the test file.