Uploading two FIT Workouts results in only one appearing

I have been creating FIT files with workout plans. The plans appear to be valid: uploaded one at a time into the Workouts directory they are usable on the device. 

The problem is that when I upload more than one file at a time only a single file results and the rest disappear from the device. 

I am using OpenMTP on Mac to perform the transfers. 

Please let me know if this is a known bug (and if it is, please fix it!) or if I should expect this to work and should experiment with other devices and software for transfer. 

thanks!