I'm experiencing exactly the same behavior, but for the match function.
Here is an example code:
$name = match (true)
{
isset ($item['label']) => $item['label'],
isset ($item['name']) => $item['name'],
default => 'Unbekannt',
};
Every time I save the file the code inside the curly brackets of the match function gets indented more.
I already uninstalled and deactivated extensions, that might cause this problem, but it didn't solve the issue.
There is also a whitespace added after isset functions inside the match function. I'm not quite sure if this is correct?