Yes it is related to your linked post. I explain it in more detail here. Unicode confuses command detection in the editor - #2 by dirk.mika1
To expand upon my post in that thread, this lower/upper case issue has the same root cause, but we’re specifically working with the Char datatype which alone cannot store a complete emoji. The case change code iterates over the selection and checks the styling of the text so that comments/strings are not impacted by the operation. When a selection consists entirely of a string or comment then case operations affect the selection and in this case it works without issue because we can allow the edit control to handle the case change natively.
I’m logging this one as we may be able to fix it safely. Generally speaking, emoji support in the Editor is limited.