I seem to be opening a can of worms here with a change I have made. The change was to plug an issue with Android 4.4 not recognising OnLayout in a custom MasterDetailRenderer.
The change was simply not having the Detail Page as a NavigationPage. I just made it the ContentPage directly. Interesting unexpected side effect of this with Xamarin.Forms.Maps which is on that ContentPage.
Before, with the NavigationPage the map when instantiated passed in a MapSpan and set the map location and zoom level. With the DetailPage just being a ContentPage now, that no longer works. The map still works ok but it initializes with a maximum zoom out no matter what. I have tried simply wrapping the ContentPage back into a NavigationPage and it all works again.
My Map does have a custom renderer also, so I have been playing with options on that level without much luck. Anyone else seen this and able to point me in the right direction?