TYPO3 Core

I'm upgrading an TYPO3 from 12 to 13 which has four page templates and according backend layouts. On of the templates is named "Default.html".

Calling a page with e.g. backend-layout/template "Article" selected + page is not from cache => "Article" is used
Calling a page with e.g. backend-layout/template "Article" selected + page is from cache => "Default" is always used

Even if I override the templateName like in the example below, "Default" is used when page is delivered from cache.

page = PAGE
page {
    typeNum = 0

    10 = FLUIDTEMPLATE
    10 {
        templateName = Article
        ...
    }
    ...
}

Deleting or renaming the Default.html fixes the problem. This only happens if an "Default.html" exists