I have an old EZX10RF, v14. I linked it to the PLM for PowerHome. I get multiple Group Cleanup Direct messages if I hold the wireless X10 button. A simple press/release and I get a single message. If I press and hold I get 3 messages. After that the remote shuts itself off so I cannot hold it long enough to generate more than 3 messages. Perhaps your wireless X10 signal is of long enough duration to produce multiple messages.
EDIT: a possible solution is to change what triggers the ISY event that turns On the ICON. In PowerHome it is possible to trigger off the Group Broadcast or the Group Cleanup Direct or both. It is normally best to trigger off the Group Cleanup Direct only as that command has command retry built into the Insteon architecture and you don’t need any logic to bypass the Group Cleanup Direct if a Group Broadcast had already been received and acted upon. Don’t know if this is possible with the ISY but I would think so.