I have found an additional piece of information for this issue - it only occurs when creating a new transaction for a previous date in the calendar window.
When using the add transaction button in the transactions window it generates the current time as normal. When adding a new transaction for the current day in the 'pop up' transactions window from calendar view, it generates the correct time.
However, when creating a new transaction for a past date in the 'pop up' window in Calendar view, it defaults to 00:00.
Can you see if you an recreate in these conditions?