Last week, I went to View -> Data Frame Properties... -> General tab to change the data frame map display units from Decimal Degrees to Degrees Decimal Minutes. (the Map Units were still in Decimal Degrees, in fact it is greyed out and can't be changed)
Today, I wanted to change the Display units back to Decimal Degrees, but after I click Apply and OK, the map status bar still shows coordinates in Degrees Decimal Minutes as I move my cursor around the map. I went back to Data Frame Properties and the Display units have reverted back to Degrees Decimal Minutes!
Why is this happening, and what should I do? Thanks.