Unexpected Quick Substitution in string literals

[Sundeep Agarwal]

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS: -g -O2 -fdebug-prefix-map=/build/bash-Smvct5/bash-5.0=.
-fstack-protector-strong -Wformat -Werror=format-security -Wall
-Wno-parentheses -Wno-format-security
uname output: Linux abcd 5.15.0-91-generic #101~20.04.1-Ubuntu SMP Thu Nov
16 14:22:28 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux
Machine Type: x86_64-pc-linux-gnu

Bash Version: 5.0
Patch Level: 17
Release Status: release

Description:

While declaring a string literal across multiple lines, a line starting
with the ^ character is resulting in some sort of quick substitution
processing.

I do not have the latest Bash on my machine, but somebody else got the same
result on the 5.2.21 version. A string similar to the sample shown below
was working as expected 3 years back. If my memory serves right, I had the
4.3 version at that time (on Ubuntu 16 LTS).

Repeat-By:

$ echo 'fig
^mango'
fig
!!:s^mango

$ echo "fig
^mango"
bash: :s^mango": substitution failed

Regards,
Sundeep