When is case sensitivity important in JSON requests to ASP.NET web services (ASMX)?
According to JSON-RPC spec, the answer is always.
9.0 Case-Sensitivity of Procedure and Parameter Names
Conforming implementations MUST treatprocedure and parameter names as beingcase-sensitive such the names bar andBAR would be seen as two distinctentities.
So, it sounds like the situations when it worked for you were the exceptions, not the cases where they didn't. Chances are someone on some side of the equation was just not adhering to the specs.