[sciurius]

This is, in fact, desired behaviour as defined in the ChordPro standard.

For guitar players, a song in key C with capo on 2 means: put the capo on 2 and play a C chord (which will sound as a D chord).
If you want the song transposed relative to the capo, in the Text Settings just click on the eye symbol right of the capo slider.
(Your workaround of sliding the slider has the same effect as clicking on the eye to enable it.)

In the Settings > Text File Settings you can enable/disable "Modulate Capo Down" according to your desire.