I have created a partial cui file that creates a new tab and a panel in the tab. This works fine.
When I try to create another cui for another plug-in I cannot get the two tabs to merge. I have set the tab Aliases to be the same but they show up as two tabs next to eachother.
AutoCAD does not merge tabs from partial CUI.
Only tabs in the main cui are considered by AutoCAD for merging based on their alias.
This post might be of some help :