tear drops disappearing during mirroring in altium
Teardrops in Altium are not treated as primitives; instead they are a sort of post-processed element that's added on top and is never really merged with the routing. When you move a trace that has a teardrop on it, that element vanishes because the original location for it has changed. Not knowing how their code is written I don't know how else to describe it. At this point I don't really have a workaround, except to simply apply the teardrops at the very end of your routing process.