I think there should be an extra leave request type of 'Work'. So you would have: Leave - for holiday/non work bits
Work - for all work related 'unpaid' leave types e.g. working from home, meetings, events, travel, training etc.
Sick - for all illness related
Currently to add travel/working from home it would have to go under leave and when it says 'approved leave' in the calendar it could easily be mistaken as holiday instead of working away - with a work type there is no confusion.