Please have a look at the attached project with a DateTimePicker configured for Time-only display. The up-down arrows is strange. To see what I mean take the following steps:
So, I started trying to increase minutes and I end up increasing hours. Same thing happens for down arrow.
Even stranger, sometimes when I press the down arrow it goes up just for once and then down for the next times. This rings a bell, so it might be a regression.
The fix was related to the Up/Down keyboard arrows (it also added PageUp and PageDown support) and broke the Up/Down button arrows. It is fixed and included in the current build which should be released tomorrow, also the Up/Down buttons are now repeat buttons – keeping them pressed repeats the click. Currently there is the development build 1.3.20 available for downloading (it still has this problem though).
Unfortunately, the fix in 1.3.18, which I just checked, was rather radical ! I mean, the wrong behaviour I described is not there any more, but now the up/down arrows do nothing! Clicking on them does not affect the control value at all. You can check it with the original attached test project.