Timetracking errors on repeating decimals

If you enter time-tracking begin and end times which result in a repeating decimal duration and save that time tracking, then when you edit the event you will be unable to save it without first erasing the now repeating decimal) duration.

To reproduce, for example,
Create an event with a start time of 8:20 and an end time of 8:40 (20-minute event). Save the timetracking event. Open it to edit. The Duration box has now been autofilled with "0.333333". When you try to save the event you will be given the lovely error "Duration (h) cannot be longer than 5 characters but is currently 8 characters long."