If user sets as default an object into the DataGroup Catalog Editor this one doesn't appear as default into the placement tool view, the system always remembers the latest item used.
Default catalog only applies when you have no "Most Recently Used" (MRU) in the user preferences. In order to see default, you must have delete your current user preferences. C:\Users\<username>\AppData\Local\Bentley\AECOsimBuildingDesigner\10.0.0
The feature is only intended to define what you see the first time you use a tool, not every time you use the tool. Once you start using the tool, the tools will show the last-used catalog item instead.