Regex case transform does not work

This has been reported here
https://forum.literatureandlatte.com/t/how-to-shift-marked-phrases-to-uppercase-during-compile/25658/1
and here
https://forum.literatureandlatte.com/t/regex-for-uppercase/35152/1

It was suggested to report this as a bug on this forum, as the solutions in the other threads don’t seem to work.

How to reproduce:
Make sure the document has a word in braces such as {word}.
Upon compile create the following replacement pattern using regex:
{(\w+)} to be replaced with \U$1

The output is Uword but should be WORD

This is on a Mac running ElCapitan 10.11.6.

Thank you!