With completion definition like

    complete -W ':bar :baz' foo

and command line looking like

    $ foo :

and pressing key <Tab>

Expected behavior: Command line changes to "$ foo :ba" as ":ba" as common prefix of all suggestions.

Actual behavior: Command line changes to "$ foo ::ba". The colon character is erroneously doubled. That prevents both further tab-completion and manual finishing of selected option.

Also:

with same completion definition

    complete -W ':bar :baz' foo

and command line like

    $ foo :b

and single press of key <Tab>

Expected behavior: Command line is changed to "$ foo :ba".

Actual behavior: Command line is not changed, bell sound is invoked.

Notes:
It works fine without the leading colons. "complete -W 'bar baz' foo" allows "$ foo b" to be completed to "$ foo ba".

Version:

• Fedora 35

  # bash --version
  GNU bash, version 5.1.8(1)-release (x86_64-redhat-linux-gnu)
  Copyright (C) 2020 Free Software Foundation, Inc.
  License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
  # rpm -q bash
  bash-5.1.8-2.fc35.x86_64

• Windows 10, msys64

  $ bash --version
  GNU bash, version 4.4.23(2)-release (x86_64-pc-msys)
  Copyright (C) 2016 Free Software Foundation, Inc.
  License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>