How to use a custom theme? Weird behavior when trying to use xmlns:xy instead of the default xmlns

[BerndBoruttau]

Hi all,

as my Avalonia journey continues I wrote a custom theme, extending the fluent theme and covering my own controls.
Up until now I used [assembly: XmlnsDefinition("https://github.com/avaloniaui", "Some.Custom.Theme")] in AssemblyInfo and <SomeTheme/> in the application styles.

In the process of unification with other libraries I switched to [assembly: XmlnsDefinition("MyLib", "Some.Custom.Theme")], xmlns:myLib="MyLib" and <myLib:SomeTheme/>.
Suddenly I get a compiler warning that the Tag SomeTheme could not be found.
If I switch back to the avalonia url it works just fine.

Any clue?

Cheers,
Bernd