The simple answer is that 'Play' is not intended for applications where you want to synchronize multiple channels of video. To the Binloop, a 'Play' command means "Play this file as soon as possible". An SPlay means "Play this file at a consistent time after I send the command". For the Video Binloop and Digital Binloop, this consistent amount of time is 16 frames by default.
It's important to mention that the 'Play' command that is available for the SMPTE trigger interface of the Binloop Config software is actually an SPlay in disguise.