Delete in Outlook.com has a bug.
Delete an email in an Outlook.com account moves it into Recycle Bin rather than putting it into the 'Deleted' folder where normally deleted emails go. It puts them in a separate folder entirely.
This has already been fixed in the current Beta version of Boxer.
It will be out for everyone in the future.
If you want to try it for yourself, visit our G+ Beta community https://plus.google.com/communities/102581534035171613663