[itsm] Agent Ticket Zoom

Hi, we are migrating from OTRS 2.4.7 to 3.0.10. We found that when the user enter the ticket and click the Free Fields link it opens in the same window, not as a popup window like the rest of the links in the menu. I had analysed through the view source option in the browser, and I found that in the link Free fields in the menu, the parameter Class is empty when it should have the value class="AsPopup PopupType_TicketAction". I have a Virtual Machine for testing where doesn't happen this. Any idea what it's happening? If i'm not clear, please let me know. Thanks. Daniel.