TYPO3 Core

After updating several sites on different servers within 4.5 LTS from 4.5.19/20 to 4.5.21 I lost the ability to use the clipboard!

Using the Web->List view I have the normal content panel with the three unchecked boxes at the bottom:

Extended view
Show clipboard
Localization view

clicken on eithoer show clipboard oder extended view doesn't change the view anymore but throws javascript errors.

Fehler: ReferenceError: invalid assignment left-hand side
Quelldatei: http://beta-....com/typo3/mod.php?M=web_list&id=181
Zeile: 1, Spalte: 60
Quelltext:
p\x3F\x26id\x3D181\x26M\x3Dweb_list\x26SET\x5BclipBoard\x5D'=+(this.checked?1:0),this);

I would rather urgent need a cliboard again. Cleaning the BE-user settings and tmp data doesn't change it, purging browser cache doesn't change anything.
Occured under FF and Chrome, seems non browser dependent.