Easy Roam FAQ's near bottom of page https://www.koodomobile.com/help/easy-roam
"[i]What happens if I have Easy Roam and I use my phone during a layover? Ex: I am travelling to Asia but have a layover in the U.S."
The answer seems to imply that both the US rate and the International rate would be added to your bill if you used your phone within a 24 hour period, firstly in the US, and then from an international destination. This can commonly occur if you call home to confirm your flight boarding in the US and a few hours later call to confirm your arrival at the destination airport.
[b]Suggestion: If within any 24 hour period, a US based call and an international based call are made, the entire 24 hour period would be billed at the higher rate. e.g $10/24-hour
This would stop the apparent double billing where a person could be charged $17 for a single day.