Solid Edge Unable to undo delete from Family of Asemblies

I have a Family of Assemblies (FOA) assembly - from this I select and delete a part.  If I try to undo this I notice that the 'Undo' icon is greyed out and I am unable to do do this.  Why?

Solution

This is working as designed.  'Undo' is not supported when deleting a part from an assembly when that assembly is an FOA file. 

Hardware/Software Configuration

Platform: INTL64
OS: windows
OS Version: 1064
Product: SOLID_EDGE
Application: ASSEMBLY
Version: V220.0
Function: FOA/AP

Ref: 002-8016725