In Tools > Customize > Menus or Context Menus, the Modify split button has an 'Add Submenu' entry which should be removed from there and added as a separate button, similar to what we did in bug 82840.
With the group button now only have a 'Rename' button in it for these two tabs, a 'Rename' button should likely be shown instead of the 'Modify' group button.
Muhammet Kara committed a patch related to this issue. It has been pushed to "master": http://cgit.freedesktop.org/libreoffice/core/commit/?id=cd7b306e614a938b7b39a66784899c22ee6f6c64 tdf#103160 Add 'Add Submenu' button in Customize dialog It will be available in 5.3.0. The patch should be included in the daily builds available at http://dev-builds.libreoffice.org/daily/ in the next 24-48 hours. More information about daily builds can be found at: http://wiki.documentfoundation.org/Testing_Daily_Builds Affected users are encouraged to test the fix and report feedback.