Hello Jose,
There are situations where you temporarily need to run several IP networks on a single VLAN. One of the common scenarios is network migration where you migrate two or more networks to a single segment. Until you readdress all hosts, to minimize the network downtime, you address the common segment using both networks and slowly migrate towards a single IP prefix.
Of course, several IP networks in a single VLAN are not separated anymore. They are logically distinct but the broadcast domain is shared by them both, and they "leak" one to each other. Most certainly, running several IP networks in a common VLAN is only a temporary measure but should never be deployed as a permanent practice.
Best regards,
Peter
