H-1 transfer, AC21 portability & concurrent payroll

[andiamo]

A new employer has filed for H-1 ("Transfer/Change of Employer") under Regular processing.

 

Scheduled to join in 10 days, but there are pending salary dues with my current employer which require to be settled, there is no formal "Notice period" though.

 

After I join the new employer, is it a problem if my current employer makes payouts to clear the balance.

 

I presume it is necessary to present latest paystubs to USCIS if requested, but is it common to have  both old and new employers to run payroll during this period

 

If not permissible, is there a better way to handle the situation, so I do not lose out on outstanding payment dues.

 

Thanks