H1 Transfer during H1 extension being processed by USCIS

Here is the scenario, my current employer files a H1 extension for me through the normal process. I assume this will take some 4-6 months to come to a decision. Now during that period i change my employer and get a H1 B Transfer approved via premiumm processing with a new employer and start working for them.

  1. Whay happens to my H1-B extension with the old employer ?

  2. If the H1- Extension gets approved after i have already started working with my new employer, will that affect my transfer petition ? Or will both the petitions be valid ?