I created a loop in the drum mode, and then wanted to add a melodic track to it, so I clicked the melodic button. This erased my drum pattern instead - would be good if they could play over each other, and would not be erased by switching.
Edit: Fixed!
I'd suggest instead of making the loop layers and editors "siblings" ontologically, instead default on app load to have a single layer, then have the option to add more layers and switch between them - add layer then edit, instead of creating a layer and adding it to a list.
I really do like the randomization though, it actually sounded surprisingly nice. Took me a moment to realize what was happening but it's actually a seemingly simple feature that's hard to achieve in full blown DAWs.
Also, did you try the preview with loop button? It's in the preview drop down. It should let you preview the grid along with what's already in the loop.