There is an inconsistency between the way tab navigation behaves before and after a panel title bar gets focus.

To reproduce this in Writer:

1) Open sidebar Menu->View->Sidebar
2) click on Page tab in sidebar tab bar
3) click on Number combobox in Styles panel (must be direct click on combobox, no click on Styles title to expand panel)
4) press tab key to tab through each item in the panel content until returning to the Number combobox
5) press shift+tab key to reverse tab through each item

Notice tab cycle does not enter panel title tab bar.

6) click on Styles title or press Escape key (focus is now on Styles title)
7) press tab key (focus is now on Styles panel title bar tool box)
8) press tab key (focus is now in panel content Number combobox)
9) press tab key until focus is on Columns combobox
10) press tab key

Notice focus returns to Styles title.

So far this doesn't seem bad but it isn't consistent.

Even less consistent/expectant is when shift+tab is used to move through panel content after panel title bar gets focus.

11) click on Styles title
12) press shift+tab key (focus moves to Number combobox, user may expect focus to move to Columns combobox)
13) press shift+tab key (focus moves to Columns combobox)
14) press shift+tab key (focus moves to Layout combobox, expected)
15) press shift+tab key (focus moves to Background combobox, expected)
16) press shift+tab key (focus moves to Styles panel title, jumps over the first combobox in panel and over panel tool box)

I would like to propose that after entering a panel content in any way, tab navigation behaves as in steps 4 and 5 and panel title tab bar is not included in tab stops. To move focus to the panel title bar use the Escape key or mouse click on the panel title bar.