I tested in Chrome and when I removed the BOM from the file and check the mode, I am not in quirks mode (document.compatMode = CSS1Compat).
Our webserver already adds a content-type header with UTF-8 specified and <meta charset="UTF-8"> was also in the HTML head. The calendar still renders with a height of 300px.
I am still working on trying to view a non-ascii character before the doctype.
Do you have any other ideas on why without the BOM it is rendering differently?