Expanding base question

[Kingfisher]

In all the games I've played, the moment I order a base expansion (be it port, airfield or fortification) to stop, the progress for that level returns to zero. No matter that the progress had reached 99%, once I stopped it and ordered it back up again (even in the same turn and the same ENG unit) they must start over at 0%.

However, something I just noticed recently has me puzzled...

Playing scenario 16 against the AI, and early on I decide to abandon Charter Towers, preferring to use the air groups and base force in other areas. Once the last plane is flown out I order the base force to march to Townsville. As they leave the progress of the airfield expansion stops at 27% and remained that way for several weeks. For curiosity's sake I then airlifted the US 91st Eng Bn to Charter Towers and sure enough the expansion resumed without missing a beat.

So, why does the same unit on the same turn have to start at zero when the expansion order is resumed, while an entirely different unit can come in weeks later and pick up exactly where the previous one left off, as though nothing happened?

[borner]

i think if you cancel it goes to zero. if you walk off or capture the base, the % is saved. Not sure, but that is the pattern I see when playing