Unit Wait and Garrison Strength

So, in one of my games, I am attacking a nation, and want to delay my units to attack some provinces right after the day change in case I can't be there to give the orders directly. The issue is, when i ordered the units to wait, the garrison strength in each province a delayed unit was in, went down to zero. The unit is still stationed in the center of said province, and when i cancel the order, the garrison strength returns to normal.

Why is that? Maybe make it so units delayed in a province count towards it's garrison strength.