Please don't assume that I assume you're a dummy! I have to ask: The stain sealer is water based or oil based? And is the 'white powder' coming through the sealer or have you already applied the lacquer? If something seems to be 'coming through', and you have lacquered over the sealer already, my first thought is that a) the sealer wasn't fully dry and so is still releasing VOCs (off-gassing) or b) the sealer and lacquer aren't playing well together (incompatible bases).

Here is a link that might be useful: HeadSpace Custom Carving and Textures