A CD/DVD on port 4 .. yup same thing happened to me too. I have a GA-890FXA-UD5 (same SB) and conecting a Samsung SH-S223C on port 4 in IDE mode is all that's needed for my system to hang on every warm boot at the POST screen. Oddly enough, the Plextors that I bought as a replacement don't hang the system when connected to port 4 but they do negotiate an incorrect DMA mode. (DMA multiword 2 instead of UDMA-5 as it should be). The same ports in AHCI mode work properly and at full speeds.
I have since changed ports 4/5 to AHCI mode as a workaround but AHCI mode doesn't always play nice with boot CD/DVD's. Sounds like a BIOS issue to me.