[danson]

You could argue it's not a bug but it is a design flaw.

When clicking on the first part of a time value (ie the Month for Dates or the Hour for times) this actually acts to 'uncheck' the field instead of focusing on the hour. This is becuase the checkbox suddenly appears pushing the data entry out towards the right of the box.

I would suggest that you make a click on the time focus the time. THEN If someone wishes to disable a field they can uncheck the value.

Alternatively always show the checkbox so you know where to click.