I have confirmed that this issue is resolved in version 8.4.2 - hidden power will now be the type-appropriate max move when used. However, before the move is selected it will display as max strike, but once selected the correct move will execute. This appears to be intended behavior - while the interaction is impossible in the main series, other moves which change type in battle follow this rule. From bulbapedia:
"If the base move's type is changed either by a move's effect or an Ability (e.g. Pixilate, Electrify, or Weather Ball), then the Max Move will also be converted to that of the new type with the same power; however, the move selection screen will still display the Max Move of the original type"