Problem with the Vaadin DateField


I am working on an application where users need to input a date using a certain date format. The users can also use the popup datepicker, shipped with the Vaadin DateField. When I run this application on localhost, everything goes fine. But when I run the same application on a Liferay server at our company, something strange happens with the labels of the weekdays and months. See screenshot. What could be the problem?

I use this simple piece of code:

DateField field = new DateField();

We are using Vaadin version 7.1.7. Thanks in advance!