Why does the 530 not record your cycling stats when in navigation mode?

Did you start the activity?

Initially, but switched it to navigation before I set off

I think what he means is... you still have to hit start when you start riding. When it loads the navigation the activity will be stopped, but the turn by turn will still work. You have to hit start after you load the route. 

It's pretty much a 'record' button - you can use all sorts of features, but if you don't hit that button, nothing will be recorded. 

I think I'll pass on the navigation feature then, I can secure my GPS to the phone holder and use that if need be. Thanks for all the responses.

You can also set Auto-Start either by reminder or actually start recording (I'm assuming both these still work when Navigating first)

Recording is separate from navigation. 

The autostart stuff will work just fine.