I just looked at the project, and I misremembered somewhat. I did add a DebugKeysMap property to JSONDictionary, but that is only used by M_JSON.ParseJSON_MTC, and has nothing to do with JSONItem_MTC.
I suppose I could change the key encoding so it tacks the hex encoding onto the original key, something like "my key-ABCDEF" (not a real encoding), but I'd have to check the performance hit of that.
I could also do something like this: "mykey" stays "mykey" while "myKey" becomes "my Key" and "my key" turns into "my key" (one space turns into two) and "my Key" becomes "my Key" (each space turns into two, each capital letter gets a space before it). Something like "MYKEY" would become " M Y K E Y".
Again, I'd have to see what the performance hit of something like that might be.