#VALUE? in MonkeyGraph

I've created a data field which uses FitContributor to record additional data for all three message types; record, lap, and session.
I've already uploaded this to the CIQ store and the values come out fine on Garmin Connect, but I am still seeing strange results for the lap and session messages when testing offline with MonkeyGraph.

For a test 2-lap activity created with the simulator, I have three tabs in MonkeyGraph: the chart, 'Lap 2', and 'Summary'.
The chart looks fine, but the Lap 2 tab has two entries which look like this:

Economy #VALUE?
Avg Economy #VALUE?


It should only have one, which should be titled Avg Economy. Just 'Economy' was the label I gave to the record message, for the chart.
Similarly, the Summary tab has one entry that just says Avg Economy #VALUE? (so the label there is correct but the value is obviously wrong)

I have verified that the messages are in the FIT file and have meaningful numbers, so am puzzled as to three things:
  • Why do the values appear as #VALUE? rather than the numbers recorded?
  • Why does the Lap 2 tab show two entries?
  • Where is the Lap 1 tab?