It appears that the mobile air units are incorrectly considered ambulances when they should be considered a fire apparatus.
The "Cancel All Ambulances" button will end up cancelling the mobile air unit and you cannot move the mobile air units between fire stations unless it has the ambulance extension. You can also move them to an "Ambulance Station" and find the unit under "Ambulance" in the fire station vehicle market. This appears to be a bug since because you can buy it from the vehicle market at fire stations as "Other vehicles" and because they are listed as "Other Fire Apparatus" on the dispatch page. The mobile air units cannot be purchased at an ambulance station, so it is odd that you can buy it at a fire station and move it into an ambulance station.
A side effect is that it will also not show the "Current station" if you purchase the mobile air unit at a station that does not have an ambulance extension.
This causes a minor problem for users who do not want to build an ambulance extension when they do not want to run an ambulance out of their fire stations.
This appears to be related to a previous report found here: errors in game