H1B transfer before Oct 1st

[hemanth7]

I work in US. My current employer H1B is picked up in lottery and is approved via premium processing. I had an offer with an other employer. I talked to their immigration team. They said, they can take the approved notice and apply for new H1B and join the firm (using my STEM OPT visa). But, they suggested that my current employer doesn't withdraw the approved H1B until Oct 1st. 

Why is that so? Since my H1B is transferred with my new employer, wouldn't my cap be with my new employer?
 

[Zodiac System]

The start date of your H1b lottery cap is October 1st.  Until then you are under CAP GAP.  

[JoeF]

You have to start working on the H1 for the original employer before it can be transferred.

The suggestion from the new employer is dangerous, and shows that the potential new employer is rather shady.

[adshah84]

You can not transfer H1b before Oct 1st. Don't do that. Just my 2 cents.