maximum values for cyclingRoadFactor

Hello,

the API documentation states that cyclingRoadFactor is clamped to the range 0.1 to 100.0. The following query:

http://www.mapquestapi.com/directions/v2/route?key=<my_key>&ambiguities=...{locations:[%2245.851013201301484,9.66646671295166%22,%2245.86228122137575,9.680843353271484%22],options:{disallows:[Toll%20Road,%20Unpaved],avoidTimedConditions:false,doReverseGeocode:false,shapeFormat:raw,generalize:0,routeType:bicycle,timeType:0,unit:k,cyclingRoadFactor:64.0,roadGradeStrategy:DEFAULT_STRATEGY,narrativeType:none}}

returns directions, while the next one (exactly the same, except cyclingRoadFactor:65.0 instead of 64.0):

http://www.mapquestapi.com/directions/v2/route?key=<my_key>&ambiguities=...{locations:[%2245.851013201301484,9.66646671295166%22,%2245.86228122137575,9.680843353271484%22],options:{disallows:[Toll%20Road,%20Unpaved],avoidTimedConditions:false,doReverseGeocode:false,shapeFormat:raw,generalize:0,routeType:bicycle,timeType:0,unit:k,cyclingRoadFactor:65.0,roadGradeStrategy:DEFAULT_STRATEGY,narrativeType:none}}

returns

"statuscode":602,"messages":["Unable to calculate route."

Why is 64.0 the maximum allowed value in this case ? does it depends on the locations ? I have an application where the user chooses the factor (through an user interface control) to decide whether favor fast roads or minor roads. In the latter case I'd like to get the directions with the maximum allowed road factor instead of an error. How can I handle that ?

Thanks

Fabio