Hi,
I am on SP7 and tried to simulate this.
I created a test Entity based on SPFLI structure. I could see the structure name SPFLI in the "ABAP Structure Name" against the entity and its properties had the "ABAP Field Name" populated with structure fields names.
I imported this into Eclipse and added an additional property and then re-imported the XML into SEGW. I was able to see the additional property and all the properties retained the "ABAP Field Name" with the structure field names. However, the "ABAP Structure Name" at the Entity level was empty.
Cheers,
Murali.