I tested 3.5.0-17.28 from Quantal and 3.5.0-18.29~precise1 from Precise-updates, the -17 kernel can suspend, but the -18 cannot.
I tested 3.5.0-17.28 from Quantal and 3.5.0-18. 29~precise1 from Precise-updates, the -17 kernel can suspend, but the -18 cannot.