Can someone tell me, are there any issues with multicast packet handling on hubs?

When we tried sending multicast packets, observed invalid packets in the capture with soruce mac address as sending device ethernet address and invalid destination mac address. Though multicast packet sent from device is of size 400 bytes, invalid packet is always of size 1518 bytes. This is not observed in switches. Unable to understand who is generating these packets. If someone has any idea please help us in this.

Hi,
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Thanks
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Within a network, which includes hubs and bridges, the relative location of a first device with respect to a subset of hubs on the network is determined. In response to an instruction, the first device broadcasts a multicast packet. The multicast packet crosses bridges and is processed only by hubs. When a hub receives the multicast packet from the first device, the hub records a first port of the hub over which the second device received the multicast packet. The subset of hubs may then be interrogated to determine over which port of each of the subset of hubs the multicast packet was received.

HUB is a dump device it can't filter the packet and do packet processing on it, It just regenerate the packet and transmit is to all other ports.