Simple Q&A D&D 4e Thread 3

[MwaO]

Q87:
I'm a Bard with Staggering Note (push an enemy 3, Ally can MBA at any point before during or after). My party has an Avenger with Power of Skill (Overwhelming Strike as an MBA, on hit he can shift 1 then slide target into his old space).

What happens when his forced movement interrupts my forced movement?

Exactly what that sentence describes — he hits the target, shifts+slides, then you continue to push him if you want to do so.

You don't have to do the whole push unless that's what you want.