External metadata injecting in wrong field

I have encountered an issue where metadata injected via external_metadata.cfg is being injected into multiple fields in the wrong place.

The issue was identified where if a metadata field name shared the same last letter as a single character metadata field, the value would be injected in both places:

ie.

external_metadata.cfg

c:"hello world" topic:"value here"

value returned from query:
c: "hello world|value here"

This could be replicated with any field name assuming the metadata name shared the same last letter.

Would this be a bug or is there any configuration setting that would cause this outcome?

Encountered in Funnelback 15.6