A year ago I opened a ticket for this problem or undocumented behavior, and received as answer:
"as this is a custom report it would not be considered supported (out the scope of tech support)."
and also:
"For Jasper Report Server documentation, you can use the "Help" button / link within the cabijs Web Console (http://help.jaspersoft.com/Default.htm#cshid=100). The free Tibco Jaspersoft community sign up may also help."
At the end; I did not find an answer for my problem