'Resource.Designer.cs' keeps old namespace after it has been changed throughout entire solution

At some point project identity was modified and i reflected that in code by renaming the solution, project, assembly and default namespace, with all corresponding folders - all instances of a name that i could find. I also used Notepad2 to fix the contents of solution and project files.
Note: Namespace in code was changed using VStudio's Rename feature.

Since then every time Resource.Designer.cs file gets re-generated, it pulls the old namespace in (?!), breaking the reference to automatic Resource class, which defines resource IDs:

Obviously, i try to fix this:

And in some cases it will immediately get re-generated again - you guessed it - with the old name, but sometimes(!) it will accept my edit, save it and let the project be actually compiled and run:

I've tried Clean and Rebuild commands multiple times for both project and solution, restarted VStudio, rebooted Windows.. No dice, it keeps happening.

App's TargetPlatform is 7.1, MinimumVersion is 4.3, all 5 supported architectures are enabled. VStudio - 15.5.4, .NET - 4.7.03056, Xamarin - 4.8.0.757, Xamarin.Android SDK - 8.1.3.0.

Just found this in the Similar Questions list: Ambiguous reference intellisense error from Resource.Designer.cs. Looked promising, so i did the following:

Closed solution in VisualStudio.
Removed entirely \bin and \obj subfolders in File Explorer.
Edited Resource.Designer.cs, so it has correct (new) namespace: J7987ca.
Added 'AndroidUseManagedDesignTimeResourceGenerator' to J7987ca.csproj, as advised.
Opened the solution, and here's the result - old namespace is back: $Re-opening solution after purging \bin and \obj subfolders$

I guess, i can start with a clean slate and re-create entire solution from scratch with a new name, but for the Love of God, why do i have to do that? And where does it pull the old name from?!

Solution

My last image shows <RootNamespace>J7980ca</RootNamespace> - the old name. I did not pay much attention to re-check that tab after re-opening solution, because such an awful glitch would never occure to me: i never had problems saving values in those VS "dialogs" previously.

It turns out that changing Default Namespace in Project Properties does not take effect!
I verified it twice.

Mind you, Assembly Name was saved, so i'm at a loss of wits to explain, how all this is happening.

As soon as i edited .csproj in Notepad2 re-opening the solution happily put proper namespace into Resources.Designer.cs and allowed compilation.