SQL Server 2014 SP1 CU6 Issue with Multi-Valued Parameters (No Longer Expand)
In case anyone comes across this, I spoke to someone at Microsoft and it turned out this bug was fixed in the next cumulative update although unfortunately it wasn't out until October. These releases which resolve the issue are: 


SQL Server 2014 SP1 CU9 
SQL Server 2014 SP2 CU2


The release date was around 17/10/2016.

We have since upgraded to the latest version which is 2014 SP2 CU2 released last month and I can confirm the issue was resolved and no longer occurs in any browser.