My situation was this: Company B offered me a position while I was employed with Company A. Company B filed for my H-1b transfer, which was then approved.
I ended up staying with Company A as Company B had to retract their offer due to the downturn of the economy. So, I never worked on the "new" H-1b, and remained on the existing one.
In my I-485 application, I did not disclose this event as I had not worked for Company B at all. They did perform a search of my records and asked me about the H-1b approval they had on file for Company B. So, in my RFE, I explained them the situation (as I did above).
I don't know what your situation is, but that was my experience. Hope this helps.