Looks like there is some smart algorithm to prevent Upper Case / Lower Case in some cases related to quotes (both single and double).
What is the reason behind this? Thanks!
I really would not like my Strings or Identifiers to be cased different when casing the surrounding code. That could mess up the program. And I think (or guess) that this was the intention for this behavior. But you can select only the content of a quoted string an upper/lower-case it. It just does not work when more than the quoted content is selected.
Before: 
After: 
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That might be the reason, thanks for your feedback!
sirskunkalot nailed it. Comments also follow the same logic.