alignment - Why are my pixels not aligning to grid in Illustrator?

I have a small Problem that occurs from time to time.

Sometimes, when I copy things or when I put an object from the symbol library on my page, the whole file gets messed up. The screenshot shows it. I make the graphic on the right, Illustrator the ones on the left.

I have pixel snapping checked. Is there a way to tell Illustrator to align everything to pixels no matter what?

Answer

Make certain Align to Pixel Grid is checked in the Symbol Options.