I have a simple system view that is used to filter Accounts into their business relationship. They can have multiple business relationships hence i am using a multi-select optionset to show this.
Eg, an Account can have a business relationship with our FX department, as well as with our Payments department.

When viewing this "Active FX Client" advanced find, instead of being shown Active Accounts where Business Relationship contains "FX Client", i am shown Active Accounts where Business Relationship is not null.
This is demonstrated pretty clearly in the below FetchXML Builder query:

Both these accounts in this list do not contain the value 1 (FX Client) and hence should not be in the list.
Now here's the kicker, when i change this to contain value 2, the filter works correctly:

So, from what I can tell so far, the issue is only when the "contain-values" is for a value of 1. All other values work.
Any ideas why this might be, or if anyone else has experience something similar?