Having quantities with decimals for invoice lines and order lines prevents a user with a locale different than english to see them.
Instead, the JSP line with the quantity for display and the formatKey="format.double" throws an exception:
javax.servlet.jsp.JspException: Wrong format string: '#,##0.00'
The exact same invoice (or order), with another user with an English local is displayed without problems. The format string is the same for both users.
The temporary workaround for these cases now is to reomve the formatKey from the orderRightBar.jsp and viewBody.jsp (invoices).