Feeds Tamper FindReplace REGEX escape backslash

Problem/Motivation

When using Find replace REGEX with a \L$1 Replacement pattern I'm getting a double backlash, like this:
- Original string: De
- Replace with: \L$1
- Output: \\LDe

Expected result: de

I have inspected the database and the config is saving the correct value, without double backslash, so I don't know where this is being made.

Thanks.

BTW:
the \L$1 is a replacement pattern to lowercase.
Some practical examples here:
https://stackoverflow.com/questions/20742076/replace-uppercase-with-lowe...