Flight creation, non HQ base.

[Wreck]

I've been trying to work this out for years but I can't figure it out. But it must be something simple...

When creating a series of flights from a non HQ base sometimes the departure airport defaults to that non HQ base & sometimes it keeps defaulting back to HQ.

There must be a sequence of events that change the default to the non HQ airport.
Its only a small irritant, but can anyone help?