Service links duplicating and disappearing on upgrade

When we Upgrade a Service, 50% of the time a Service Link is dropped from the previous Upgrade, the other 50% a second duplication link is added to the list.
I cannot see why, nor know what to look for to help further.

Steps :

  1. Select Upgrade
  2. See that a Service Link is Missing/Duplicated
  3. Fix as required
  4. Click Upgrade button
  5. Goto 1

Versions :

rancher/server:v1.2.0-pre4-rc6 host1
rancher/agent:v1.1.0-rc7 on hosts1 and host2

I have raised a GitHub issue here as well: