I have setup where the centerRegion of a N,S,E,W Viewport contains a tabPanel (4 panels).
It appears that while tabbing from the northPanel into the center tabPanel, the cursor ignores the first panel and gets set directly into the first field of panel content instead of the panel tab itself.
After tabbing completely through the content, the cursor will end up on the first tab.
Bizarre. I have a similar situation on the same screen the does not do that. The cursor properly traverses through the tabs in the tabPanel before entering into the active panel content.