Right clicking the Titlebar and selecting "More Actions" provides a menu containing a "No Borders" tick box. However, this item is missing from the corresponding menu when right clicking the taskbar button. As a result, once ticked, this box becomes inaccessible and there appears to be no way to restore window decorations. Reproducible: always Expected behaviour: it would be possible to access this item through the taskbar menu to deselect it.
The menu can be accessed by Alt+F3, so there's no need to have the option available elsewhere.
*** This bug has been marked as a duplicate of bug 374092 ***