I monitored my calls for the last few days (holiday time, gotta call mom,etc). My call volume is not at the maximum and I don't think it changed from one call to the next. The latter is harder to figure out without doing specific testing, like ending a call with the volume very low. But the volume was definitely not all the easy up.
Strange issue. Understand your frustration, especially with the volume rocker being a pain to use.
Update: just did a test call. Volume at 1 click from lowest. Setting was maintained for next call.