When you doubleclick on a tab header the whole ribbon area collapses only leaving the headers visible.
If you then click on another header the ribbon should become visible again immediately, but using XamRibbon it takes several seconds!
Also doubleclicking again to un-collapse the ribbon also takes several seconds.
Bug?
Using Infra 11.1
It's hard to say based on the information provided. It could be that there are lots of handled exceptions that are slowing things down or it could be that you have lots of elements. Please provide a sample that demonstrates the issue and we can look into it further.
As this also only happens when executing in VS2010's debugger I'll mark this as solved.
Also see
http://community.infragistics.com/forums/p/57535/293479.aspx