Changing meter from 4/4 to C results in changing pickup measure to full measure

I wanted to set up a chorale score that is supposed to have a time signature of C. However, C is not available when setting up a new score. Only time signatures as meters are available.

So I started the score up with 4/4 time and figured I'd change to C (common time) when I got started. I required a pickup of 1/4. C is equivalent to 4/4 but is used as an alternative and in older music.

However, when I finished the initial setup and went to change 4/4 to C, the pickup measure was changed to a full measure's value. I had to manually change the measure property actual duration back to one quarter.