If the attributepanel is detached, you cannot delete a feature by pressing the <del> on keyboard.
True. However you can delete selected features by using the right click menu.
true for all attribute windows as shortcuts are executing plugins. the copy/paste/extract/delete plugins currently do not know how to deal with selections in foreground attribute windows.
as an extra issue, these shortcuts Strg+C/X/V or Backspace/Del interfere with editing possibilities in the attribute table when editing cell content.
afair - current workaround is to completely disable OJ shortcut execution if a attribute window is the active window.