Sn_IR_SENDOK received but data not sent immediately

I’m putting together an Arduino DHCP bootloader for the 5500. It works fine but on boot the initial DISCOVER packet is not sent immediately after the Sn_IR_SENDOK is received. It’s sent after about 10 seconds and I can see that the Link Status bit changes from 0 to 1 at about 5 seconds but even then it takes a while for the packet to be seen on Wireshark. After this everything clicks into place.

Is this behaviour expected? I have explicitly set OPMDC to 100T/Full/Auto-Disabled.