Command substitution before while loop

[Krystian Wojtas]

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-musl
Compiler: gcc
Compilation CFLAGS: -g -O2 -Wno-parentheses -Wno-format-security
uname output: Linux bc55e8b47896 5.3.0-42-generic #34~18.04.1-Ubuntu SMP Fri 
Feb 28 13:42:26 UTC 2020 x86_64 Linux
Machine Type: x86_64-pc-linux-musl

Bash Version: 5.0
Patch Level: 16
Release Status: release

Description:
        Making comments in pipes using command substitution is very helpful. 
But there is syntax error it it is done just before while loop. Could it be 
considered as bug?

Repeat-By:
        Script is attached. Ouput
bash-5.0# ./comments.sh
message
message
./comments.sh: line 20: syntax error near unexpected token `do'
./comments.sh: line 20: `while read variable; do'

Best regards,
Krystian Wojtas

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comments.sh
Description: application/shellscript