My Friend,

Same situation i encountered when i joined here at Qatar i came originally in Dubai when i got a job offer here in Qatar, i forwarded all my educational certificate to my present company (Qatar) after 3 weeks employment visa was been released (Qatar) and that same date, i formally submit my resignation letter to my previous employer.

It means Dubai can issue visa without cancelling your Qatar visa but it need and necessary to cancel for your final settlement to your company and to the bank.And it need to be cancel (Qatar visa) so you can enter UAE, because dual visa is not allow.

Hope this help.