Circuit Basher - you were probably not advised to select Standby on your transponder whilst flight training in Canada because the Canadian AIP clearly states -
"Do not select "STANDBY" whilst changing codes as this will cause the target to be lost on the ATC radar screens"
Perhaps it's an airspace thing, in the congested UK there's presumably a lot more primary radar coverage so contacts are not as readily "lost" as in the wide open spaces of North America where p'raps there's more reliance on SSR. Any ATCOs from t'other side of the Atlantic care to state their preference?