coproc does not work with a lower case variable name

[gd]

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS: -O2 -Wall -D_FORTIFY_SOURCE=2 -fstack-protector-strong 
-funwind-tables -fasynchronous-unwind-tables -fstack-clash-protection 
-Werror=return-type -flto=auto -g  -D_GNU_SOURCE -DRECYCLES_PIDS -Wall -g 
-Wuninitialized -Wextra -Wno-switch-enum -Wno-unused-variable 
-Wno-unused-parameter -Wno-parentheses -ftree-loop-linear -pipe -DBNC382214=0 
-DIMPORT_FUNCTIONS_DEF=0 
uname output: Linux as.lan 5.14.14-1-default #1 SMP Thu Oct 21 05:05:03 UTC 
2021 (2b5383f) x86_64 x86_64 x86_64 GNU/Linux
Machine Type: x86_64-suse-linux-gnu

Bash Version: 5.1
Patch Level: 8
Release Status: release

Description:
        coproc gives a syntax error if I try to use it with a lower case 
variable name and a compound command:
        bash: syntax error near unexpected token `}'
        bash: syntax error near unexpected token `('


Repeat-By:
        coproc bc { bc; }
        coproc bc (bc)