Indeed, the SharePoint calendar does not like the date/time format. Hilary has come up with a nifty workaround: using FormatDate to set the dates to "u" format, meaning that now they'll have Z at the end. SharePoint seems to like this format. Here's the command:
concat("FormatDate /date=", <datefieldhere>, " /format=u")
I'm attaching a sample form which you can look at in design mode. Let us know if you run into any questions!