Bug 83291

User has three lifelines and 'Set Width to Message Width' option is set to true
for two pairs of names (for neighbour elements).
There are an indicator bars in the track between the element names.
But if user moves middle element to the right, one of indicator bars disappears.

issue is visible in 'UML Modeling: Creating Sequence Diagrams' tutorial.
How to reproduce:
- create sequence diagram
- put three lifelines on diagram
- right-click in the track between the left and middle element names.
In pop-up menu Select 'Set Width to Message Width'.
An indicator bar (looks like '(---)') appears in the track between the two
element names.
- Select the same ''Set Width to Message Width' for middle and right elements.
- in diagram move middle lifeline element to the right (but still between left
and right elements).

ISSUE: An indicator bar between middle and right elements disappears.