User690216013 posted
Is it intentional, that this behaviour changed between IIS 7.5 and IIS 8.5?
IIS Manager source code is almost the same, except that IIS Manager on IIS 7.5 uses .NET Framework 3.5 while on iIS 8.5 uses .NET Framework 4.x. So I assume the XML validation difference comes from .NET Framework itself.
Will there be an update
Not likely. Windows Server 2012 R2 is out of mainstream support (since 2018), so only security related issues will be fixed.