Octave (8va) for 'two hands' playback

I've added an octave line satisfactorily to a section of my music for piano, but I've edited the beginning text to say "8va both hands". However, the playback functionality doesn't necessarily pick up on playing both hands/clefs one octave up... it just applies it to the treble clef line.

Does anyone know if there's a way (or what I'm not doing) to somehow select or apply the 8va effect to both lines for it to play back correctly?