After upgrading OTRS and ITSM from 4.x to 5.0.19 I've stumbled into the same problem, following the guidance from the thread http://forums.otterhub.org/viewtopic.php?t=33930
(and a lot of debugging later) in
SysConfig -> ITSM Configuration Management -> Frontend::Agent::ModuleRegistration -> Frontend::Module###AgentITSMConfigItemZoom
you have to add ITSM.Agent.ConfirmDialog.js (as per the linked thread) AND Core.Agent.LinkObject.js.
This fixes the navigation links in the page.