I've looked into this issue some more (DEGN8RFC3B).
The problem occurs when the XPage root control has dojoForm="true", and you have an xe:djTabContainer or Dojo Tab Container (dijit.layout.TabContainer) within an area that is partial updated or partial refreshed.
// needed in 8.5.3
// needed in 8.5.3 and 8.5.4
In 8.5.3 you need to call both startup and resize. In recent not-yet-released 8.5.4 builds, you only need to call resize.
The updated sample is attached.