Hello Pavel:

You'll be pleased to know that we have addressed your issue in dhclient in our upcoming feature release, 4.4.0, due out the first quarter of 2018.  By default, dhclient will now wait 10 seconds after sending a DHCPDECLINE prior to sending a DHCPDISCOVER.  This behavior can be altered via a new command line argument, --decline-wait-time <seconds>.  This argument allows you to specify the time to wait, including 0 which means do not wait at all.

We like to acknowledge our contributors by thanking them in our release notes.  If you wish to recognized in this manner please respond with how you wish to be identified.  

Thank you for taking the time to report the issue to us. 

Regards,

Thomas Markwalder
ISC Software Engineering