When configuring a calendar form field with the parameters default="NOW" and filter="user_utc" (or server_utc) it will result in the wrong offset. For example, in my case the server (and user) are in the timezone Europe/Berlin which has a +2 offset to UTC.

The fix is simple: Set the default timezone to "UTC" and restore it afterwards when the default="NOW" is set (together with a filter). Similar is already done in the JDate class constructor.

Note: I wasn't sure where to open it, since this is a platform issue but I'm confused as to where it has to be reported (i.e. the platform repo has no issues, is it dead?). The framework repo adds to the confusion...