Item8024: ExtensionsRepository including FosWiki breaks SubscribePlugin when running 4.2.3

I have a stock 4.2.3 install and tried and failed to install SubscribePlugin:

$TWiki::cfg{ExtensionsRepositories} = 'TWiki.org=(http://twiki.org/cgi-bin/view/Plugins/,http://twiki.org/p/pub/Plugins/); Foswiki.org=(http://foswiki.org/Extensions/,http://foswiki.org/pub/Extensions/)'; 

And added:

Fetching http://foswiki.org/pub/Extensions/SubscribePlugin/SubscribePlugin.tgz...
Unpacking...
SubscribePlugin_installer
pub/
pub/System/
pub/System/SubscribePlugin/
pub/System/SubscribePlugin/wikiringlogo20x20.png
lib/
lib/Foswiki/
lib/Foswiki/Plugins/
lib/Foswiki/Plugins/SubscribePlugin.pm
data/
data/System/
data/System/VarSUBSCRIBE.txt
data/System/SubscribePlugin.txt

Error: Installer returned errors:

Undefined subroutine &Foswiki::Extender::install called at /home/wiki/htdocs/twiki/SubscribePlugin_installer line 141.

You may be able to resolve these errors and complete the installation from the command line, so I will leave the installed files where they are.
Installation finished.

Note: Before you can use newly installed plugins, you must enable them in the "Plugins" section in the main page.

I'm unclear: I thought we were supposed to use both the Foswiki and TWiki repos for now, but, if so, this is broken for SubscribePlugin.

---

Thanks to WillNorris, who told me that TWiki shouldn't be given the FosWiki repository, I'm closing this.

M.