Edge 840 Workout Screen not remembering data fields

No matter what I try or how I customise it, the Workout screen on my 840 Solar always reverts back to the default layout. 

For example, I want to replace the 'Step Distance' data field with something else - Speed let's say. Then the following day, it's lost all my changes and I have to customise it all over again. Doesn't sound that bad, but when you're doing daily workouts this is a chore.

Has anyone else experienced the same and if so, have you managed to resolve it, or have any suggestions I might try?

Thanks..Ed