git-develop in ispconfig_update.sh not working

Looks like the option git-develop don't donwload anything:

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Note: On Multiserver systems, enable maintenance mode and update your master server first. Then update all slave servers, and disable maintenance mode when all servers are updated.

Select update method (stable,nightly,git-develop) [stable]: git-develop

Downloading ISPConfig update.
Unpacking ISPConfig update.

gzip: stdin: not in gzip format
tar: Child returned status 1
tar: Error is not recoverable: exiting now
/usr/local/ispconfig/server/scripts/update_runner.sh: Zeile 60: cd: install/: Datei oder Verzeichnis nicht gefunden
Could not open input file: update.php