libreoffice-kde5 / libreoffice-qt and Kvantum themes

OS: Kubuntu 19.04
LibreOffice: 6.3.1.2

I'm developing a Kvantum theme. At the same time I'm looking at different
Kvantum themes to understand how to implement the widgets showing in
Libreoffice toolbars, and most importantly if it makes sense to even invest
time into it...

Here is a screenshot [1] of Libreoffice with Tabbed user interface: a
comparison between libreoffice-gtk3 (with Qogir dark theme) vs
libreoffice-kde5 (2 different Kvantum themes, FlatBlur-Blue [2] and Oxygen
which comes with Kvantum source code).

A few glitches are showing up in the KDE5/Qt packages:

   1.

   Vertical separators are not visible in both Kvantum themes. Maybe this
   widget has not been coded yet?
   2.

   Comboboxes's dropdown arrows appear to be detached from their respective
   comboboxes.
   3.

   Tabs are not rendered correctly. From the light Kvantum theme we can
   clearly see the first and last tabs should be swapped. From the dark
   Kvantum theme, the bottom border of the active tab should not being
   rendered.
   4.

   Kvantum allows the use of transparency: the dark Kvantum theme used in
   the screenshot heavily relies on trasparency: that's why it looks so ugly
   in Libreoffice. It is extremely difficult to develop a transparent theme
   that also looks good when transparency is not enabled... As of now,
   libreoffice-qt / libreoffice-kde5 do not support this feature. Can we
   expect situation to change in the future?

[1] https://i.redd.it/5ghahkgb8pr31.png
[2] https://www.pling.com/p/1326672/
Davide.