Tag - Filename conversion breaks with single/double backslash

Environment: Windows 11 22000.795, Mp3tag v3.17 32-bit

Title: I still think about y%#'()_*{\\""'&36)%(""'$&''&(15y!!!_??*`~

Format string: %title`, `$validate(%title%,)

Expected behavior: Removing illegal characters.
I still think about y%#'()_{'&36)%('$&''&(15y!!!_`~

Actual behavior: Truncating all starting right before double backslash.
I still think about y%#'()_{

Changing double backslash to single backslash:
I still think about y%#'()_*{\""'&36)%(""'$&''&(15y!!!_??*`~

Format string: %title`, `$validate(%title%,)

Actual behavior: Backslash doesn't get removed in preview,
I still think about y%#'()_{\'&36)%('$&''&(15y!!!_`~
and creating folder I still think about y%#'()_{ with filename '&36)%('$&''&(15y!!!_`~.flac

See here:

and the documentation:

The backslash is no invalid character that has to be removed.

What you call

is fulfilled - in accordance with the documenation.
No bug.

Thank you for information. However even with $replace, text after double backslash \\ is removed.
test\\1234 -> test
test\1234 -> test_1234

could you show an example?
Generally, MP3tag displays multi-value fields with a double backslash.
CHeck the extended tags dialogue Alt-T to see that you have several fields of the same type.
To merge such fields, you need the $meta() functions, where you preferably set a different separator than the double backslash.

More like edge case; the title itself contains double backslash.
From first post: Title is I still think about y%#'()_*{\\""'&36)%(""'$&''&(15y!!!_??*`~
For testing, set title to test\\1234, $replace(%title%,\,_) or just %title% shows test only

As soon as you enter data with a double backslash and save that modification you create a multi-value field.
So check the extended tags dialogue - you should have now 2 fields of the type TITLE, one with "test", the other one with "1234".

In windows, empty folder names are not allowed - a double backslash would create such an empty folder name.

Didn't know that double backslash works as seperator.. that makes sense. That's intended and no way to disable or get around right? I'll have to use other software for the file. Thank you.

One way around it would be to merge the duplicate fields into 1 with a different separator than the \\
The semicolon usually works ok.