In my report, the StartDate parameter’s default value is toDate(‘2016-11-01 00:00:00’).
If I drag the StartDate parameter onto the report designer and set the text component’s date format to d-MMM-yyyy HH:mm:ss, the preview displays 31-Oct-2016 23:00:00.
If I add a string parameter and set its default value to dateFormat({StartDate}, “d-MMM-yyyy HH:mm:ss”) and drag it onto the designer, the preview correctly displays 1-Nov-2016 00:00:00.
Hmm… not sure what’s going on then. I’d suggest emailing/calling support and have them work with you on it, since they are set up to reproduce this a bit better than I am.