Wait Doesn't Wait?

I have found that wait(), Playback() and in fact almost all of the statements in a dial plan have the following text posted after them (in verbose mode): “in new stack”. Can someone please explain what “in new stack” means? I’ll search the code, but I wondered if anyone knew off the top of their head.

My 2nd question is this: Are these being launched in new threads? That is how they are behaving, and if so, that is bad news for me. If so, can this behavior be changed or is there a way around this?