This gets really rough with middle school. If I had to combine classes my morning classes would be:
1st - 35
2nd - 45
3rd - 55
4th - 45
I'm exhausted by lunch. If we don't expect core content to cover classes and combine (if they do, that's a different conversation to have) and if want to validate ourselves as equally important as core content, we shouldn't be ok accepting this additional workload.
As a final point to what I've seen other responders post, if your HD is using local days, the district has full discretion to look into why he's taking off or not approve the days.
TL:DR - Yes, you're right to be disgruntled. However, fine a way to release the steam or the resentment will fester.