Created attachment 167035 [details]
Detail of bottom-Right corner

It occurs in Calc and in Impress; also in Writer when document is zoomed to be larger than window and the horizontal scrollbar becomes visible.
In Calc, the right-end of horizontal scrollbar has no arrow-button, only the kind of separator button used to split the window. In Impress and Writer, it has a blunt end (in these components it is not possible to split the window).
In Calc, when the window is split, both the left and the right panes will show the same bug: horizontal scrollbar with no right-arrow button and terminating with blunt end (in this case, as in Impress and Writer, it is not possible to further split any of the "sub-windows").
I use KDE interface (Kubuntu Bionic, 18.04). Tried installing libreoffice-gtk3, or libreoffice-kde5 and libreoffice-qt5, always with the same result.
Vertical scrollbar works fine: on top, the little button that splits the window, under it the top-pointing arrow button, further down the "body" of the bar with its "thumb", and then at the bottom end the bottom-pointing arrow button.
This bug is not critical, but it is annoying when using sheets with many columns some of them very wide: the "thumb" button on the scrollbar produces very large displacements, the arrow button at the end moves the sheet one cell at a time.