DH55HC - serial port problem (via header)

I put together machine with DH55HC (Core i3-530) and run gentoo x86_64 on it. I have problem getting the serial port work, using standard serial port bracket. So far I:

• checked wiring on bracket and DB9 and intel doc (matched)
• checked in BIOS serial port is enabled (enabled)
• connected two different devices (GPS and APC UPS) - (failed)
• connected same device vie USB->serial adapter (using pl2303 driver) - (both work fine)

Linux kernel detects at boot two serial ports:

kernel: 00:09: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A

kernel: 0000:00:16.3: ttyS1 at I/O 0xf0a0 (irq = 17) is a 16550A

I expected the first one is the one on the board, but tried both (and wonder from where comes the second one). I am willing to investigate further, but currently do not have any idea where to go. Can anyone help me?