I would be the other way, they should NOT hold a HA room open while any member is wanting to book that room. This is not a flaw, it's the way it should be and the way hotels do things as well. However, if there is a room available and all the HA units have not been accounted for, one would be set if they needed a HA room. It could also happen where you needed a HA unit and a room was available but not a HA unit. They should NOT simply hold the HA units open just for those that need one like a parking space is HA or no one.
They don't allocate specific rooms on booking except for HA designations.
That is not true if I understand what you're saying. The rule is that you must have so many HA rooms available with a few other caveats. They only designate certain specific units for HA on booking and then assign the rest at the resort either a few days before arrival or at check in depending on the resort and whim of the staff. They can move unit assignments around but they will not force you to move once checked in to a unit and they will not take away a reservation. If there were 100 units with 10 HA units and all 100 units were booked but only 5 were booked as HA need, one who needed a HA accessible unit can't get a unit because they're all booked already. They will not take a reservation away from someone else.
DVC in general has too many HA units overall, this is why those HA are forced on guests not uncommonly. Personally I'd rather not go to WDW or anywhere else than have a HA unit. Someday I may need it and I'd be glad to have the option.
Exactly what I was saying, thanks for saying it better.