TabPanel second tab acting strange RPI /Linux

Ok folks, another stupid question / observation:

I am using the TabPanel. I have 2 tabs (so far)
On windows, tab0 and tab 1 are the same size on
window1. On the RPI / Linux, the second tab panel is
about half the size as Tab0. I see no way to set the
size of the tab panels - but somehow it shrinks from
Tab 0 to Tab 1.

What am I missing?