I bought a Palm Pre on the first day and it always worked fine with Zimbra mail and calender using EAS. It did break with the upgrade to 1.3.5 and I have now upgraded to 1.3.5.1 The calendar doesn't sync any longer. It does show grey boxes as though it were illustrating free and busy times.
I have used webOS Doctor for Palm Pre from sprint to reinstall and have no patches, themes, etc.
Any ideas?