When a ribbon band collapses, a special KeyTip is used to
open a popup with its content. This KeyTip can be set with
setCollapsedStateKeyTip. That works fine. But in the popup,
the KeyTips are not shown. They still work, but you have to
guess them. This looks like a bug to me.
You can reproduce this with the Ribbon test webstart. In
"Page Layout" (P), the "Clipboard" has "Paste" (V). In
normal state, pressing Alt,P,V works. When you resize the
windows to a small size, where the "Clipboard" changes to
collapsed state, you can see (ZC) for the "Clipboard". The
popup opens, but no KeyTips are shown. But Alt+P+ZC+V works.