Error message is missing from API refresh history

The API to get refresh history does not include the error message for failed refreshes. If you look in the service and view the history you'll see something like this:

Underlying error message: AnalysisServices: The connection either timed out or was lost.

or this:

Underlying error message: AnalysisServices: Server: The operation was cancelled because of locking conflicts.

(both very helpful)

However if you pull the refresh history from the API you only see this (the exact same message) for both failures:

'serviceExceptionJson': '{"errorCode":"DM_GWPipeline_Gateway_MashupDataAccessError","errorDescription":"-2147467259."}

(not very helpful)

We need the 'Underlying error message' to surface in the API.