Find all references (now called 'Find all usages') finds all places where the entity is used directly. Passing a variable that has as its type that entity is not a direct usage. The place where the variable is defined (via a retrieve, create or as a parameter) is the direct usage and will be found by 'Find all usages'. So the fact that you do not find the calling of the web service as a usage is correct and not a bug.
However, I can imagine that you want to find all places where a variable of a specific type is being used. For that reason, I have added a feature called 'Find Usages of Variables'. This feature will appear in version 2.5.2 of our technology.