Writer: unable to dock subpanel in sidebar

I performed a general upgrade on my machine, going to Fedora 24 (without Wayland) and installing LO from a package.

I can no longer dock multiple panels (e.g. styles and navigator) in the sidebar. I followed the magic stance in this related question, but it no longer works here.

I looked at the OpenGL settings, but now TollsOptions... LibreOffice says OpenCL (C for Charlie), not OpenGL (G for Gulf). I don’t know if it is relevant. Anyway, I checked it off and rebooted to no avail.

I noted also a strange thing in the UI. LO does not seem to retrieve the OS window style and reverts to “pure” (?) X UI items as can be seen in the following screenshot:

The scroll bars have no arrows for line up/down. If you click in the scroll bar outside the black position indicator, you do not get page up/down action but a direct jump to this “absolute” position (top is first page, bottom is last page and intermediate clicks warp you to the designated page).

I tried changing the UI theme from the OS settings but LO behaviour remains the same. I suspect some kind of incompatibility with recent modifications in KDE (related to Qt5?).

Has someone experienced the same inconvenience? Is there a workaround?