Backslash mysteriously disappears in command expansion when unescaping would reference an existing file

[Charles-Henri Gros]

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS: -g -O2
-fdebug-prefix-map=/build/bash-Dl674z/bash-5.0=.
-fstack-protector-strong -Wformat -Werror=format-security -Wall
-Wno-parentheses -Wno-format-security
uname output: Linux d-us6a-ubuntu-03 5.0.0-13-generic #14-Ubuntu SMP Mon
Apr 15 14:59:14 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
Machine Type: x86_64-pc-linux-gnu

Bash Version: 5.0
Patch Level: 3
Release Status: release

Description:
        Backslash mysteriously disappears in command expansion when
unescaping would reference an existing file

Repeat-By:
        > touch a\$.class
        > for i in $(echo "a\\\$.class"); do echo "$i"; done
        a$.class
        > rm a\$.class
        > for i in $(echo "a\\\$.class"); do echo "$i"; done
        a\$.class

The existence or not of the file should not have any effect.