Triplet tremolo playback with "section" patches (violins, violas, etc.)

I am trying to recreate an eighth-note triplet tremolo, similar to the attached image. When I play back the tremolos using a "section" instrument patch (i.e. plural violins, violas, 'celli, and basses), it instead plays what sounds like a nontuplet. All of the standard instrument patches (flute, piano, even single violin/viola/etc.) seem to work correctly. I've attached a picture of the score I'm attempting to recreate as well as a sample mscz file that displays the issue I'm referring to.