With custom DateTime Format, the DateTimePicker shows no reaction on clicking the spin buttons or pressing the Up-/Down keys. The manual entry of a value gets lost when the control loses focus, as reported in Issue 18624, (which was already fixed, but obviously for default format only).
__If additionaly, the Custom Format string is not set, the whole application crashes on any attempt to spin the value!__
Comments: ** Comment from web user: emartin **
__If additionaly, the Custom Format string is not set, the whole application crashes on any attempt to spin the value!__
Comments: ** Comment from web user: emartin **
Correction:
Using this (weird) timeformat:
yy*dd h:tt
the spin buttons are working, but the manual entry doesn't.