SSMS 17.3 IntelliSense collation-related validations do not adjust for Contained Databases
When validating T-SQL syntax with respect to collation-dependent behavior and the active / current database is partially contained, IntelliSense does not properly adjust expectations: it applies the server-level or database-level collation. Specifically, object (local and temporary) name resolution, and variable name resolution are not using a collation of Latin1General100CIASWSKS_SC, but they should.
This results in situations where:
there is a conflict due to case-insensitivity (or accent / wide / kana -sensitivity) that is not being flagged, or
an item is flagged as being in conflict, yet there is no conflict and it will actually function without error.
Solomon Rutzky commented