Values assigned to property does not show assignments

I have a auto property defined:
public TaxDefinition TaxDefinition1 { get; protected set; }

I want to find where the set is referenced, so I click on a use of the property, and right click Inspect->Value Origin, eg

     foo(GlobalTestData.TaxDefinition1);

I get the following:

property TaxDefinition1
Return value of getter of property TaxDefinition1
[GlobalTestData_Web3Sample.initialise]  TaxDefinition1 = Web3TaxManager.Instance.GetTaxDefinition(499)
[StandardWeb3TaxManager.GetTaxDefinition]  return taxDef
Analyzing...
Values assigned to property TaxDefinition1

Note that "Values assigned to property TaxDefinition1"  is blank - it doesnt spot the assignment reference which is listed in the "Return value of getter of property TaxDefinition1"

whats going on here?