What's happening: When my custom SCV builds my custom barracks, the moment construction starts a fully built barracks model appears and starts blasting out fire jets as if the barracks is flying. However, the Terran building animation still plays out underneath the flying model properly.
What I've tried: I've looked over the barracks actor many times and the events seem fine. I've even removed every single message that correlated to flying, with no luck. I've tried hiding the actor until construction was complete, but that also hid the building animation.
Are you sure it's the flying animation and not some dust/spark effect from the obscured build model?
There are some actors linked to the build ability, search for "Build" or "Construction". One controls the scaffolding model and one acts as an Event Macro to time the "pop-up" animations of the building itself (it's a hardcoded "auto-key" feature called a Progress actor, not an outright Event Macro).
I believe one of them, a Model type iirc, has a list of "unit contruction start" events as the main initialisation, you have to add any custom buildings you create to the appropriate list. There's 3 separate setups for different build sizes. Terran structures also had a UnitConstruction->Create "StructureName"Build, each referencing a unique actor (i.e. BarracksBuild in your case), I don't remember what exactly they do but they might link into that construction setup too.
Thanks Photoloss, I managed to get it working with your advice.
I had the Terran Building Build Actor properly cloned, since I noticed that in the Barracks actor. But I had no idea about the Terran Construction "progress" actor. I just needed to add my custom SCV build ability to that list, and voila.
It was actually a lift-off animation that was playing before, not fly, as I found out.