Hi Ben,
I think this is because the oData Model doesn't support the two-way-bindingmode, but the JSON Model does.
The two-way-bindingmode describes that changes will be applied in the direction from model to view and vice versa.
You can look it up here:
https://sapui5.netweaver.ondemand.com/sdk/#docs/guide/UsageInApp.html
Regards,
Jan