If you have multiple lines selected (connected exploded arc segmnents or a series of lines), then if you copy the length in the entity info box, it will corrupt the lines or change one of their lengths by small and large amounts randomly.
It looks like the ability to copy the value in a read only Entity Info field was added to 2025. The vertex moving when you click back into the model space only happens in 2025 and later. I logged a bug report, SU-63553.