The menu-option for TaskPane isn't available in the view-menu.
When you customize your menu you can still add it. But it has been removed in 94b868141e5ad43f8e2affb77563ec0f999a2d60 for the new sidebar. But that has been disabled in 4.1-series.
Submitted a patch for 4.1-branch:
thanks Rob :)
*** Bug 68160 has been marked as a duplicate of this bug. ***
This menu item is also missing in Writer\Calc (used by some extensions), as mentioned in bug 68160. You can see it also in the commit which removed it: http://cgit.freedesktop.org/libreoffice/core/commit/?h=libreoffice-4-1&id=95ae39c0c34c9a5e6fa6e72bf3a631a9a799b872
Fixed in https://gerrit.libreoffice.org/#/c/6943/
*** Bug 72719 has been marked as a duplicate of this bug. ***
*** Bug 73784 has been marked as a duplicate of this bug. ***