I've been fighting with a certain behavior for a while, where our customers are complaining that when they select a tab it scrolls the bar to a completely different tab. Turns out that I can reproduce the same behavior in your sample app, so I'm thinking it's a bug in Navigator, not in my code.
Steps to reproduce:
1) Start "Singleline + Multiline" demo application
2) Select "Singleline" radio button
3) Click right-arrow to scroll the tabs to the right.
4) Click "Page 6"
=> Watch the tab be selected and then the tabs instantly being scrolled back to the first tab.
The unwanted scrolling to a non-selected tab happens whenever a new tab is select, and the previous tab did not have focus (i.e., the focus rectangle was not drawn around it, but focus was either inside the page, or somewhere different altogether)
Any chance you could confirm this? (And maybe suggest a workaround or give an idea on a fix?)