FYI, the compat layer files were updated and a new zip file posted earlier today (download). There was one fix for a breaking change due to an internal 4.0.1 change that affected a grid override, but most everything else is just additional aliases that did not exist before and a few other minor fixes.
If you aren't having any major issues with the original compat files then there's not much need to upgrade, but if you're just starting or having issues you should try the newest version.
In ExtJs3.x I had a button which added a panel to a tabpanel. This panel had an id, so when I clicked this button the panel was only added to the tab panel if a panel with that id did not already exist.
This does not seem to be the case in ExtJs4.
(i.e. I can add multiple panels with the same id to a tabpanel in ExtJs4. )
Has this behavior changed?
If so, how can I replicate the behavior of the tab panel in ExtJs3.x?