There’s a bug when using imperial (foot/inch/fractional) measurements in the Measurement box when model units are set to any metric unit.
See SU doesn't recognise fractional inches (e.g., 1/2") as an imperial measurement when units are mm
for some of my observations about this.
You shouldn’t ever get a rotation, instead of an offset, as a result of anything you type, but if you just type 1/2 when units are set to (for example) cm, you get 1/2 a centimetre.
If you use 1/2" you’ll probably get half an inch.
But use a mix of feet and inches with inch marks ("), or mix inches and fractions, and you get a confused mix of inches or feet, and mulitples or fractions of the metric units!
Seriously bugged.