if_re regression on RELENG_8

Hell Low.

When Vista finally died on my girl's notebook,
she asked me to install FreeBSD on it, so no more viruses.
I installed RELENG_8_0/i386, to compile fresh RELENG_8/amd64
in hopes SUJ will be availible (2gb RAM is kinda too small for ZFS).

I've built custom kernel (GENERIC with unneeded things nodevice'd)
and rebooted it, kldload if_re, ifcionfig, so ping started to work.
I then attempted to mount_nfs, but it hung.
"re0: watchdog timeout" appeared on console.

So the thing is, re0 stops working after sending any packet
longer than 536 bytes. I tested via ping, -S (536-8) works,
but (537-8) leads to watchdog timeout. The host cannot be
software rebooted in ~80% cases after it happened.

Machine in question is Fujitsu-Siemens Amilo Pi 2540.
The lines from RELENG_8 dmesg are:

re0: <RealTek 8101E/8102E/8102EL/8103E PCIe 10/100baseTX> port
0x3000-0x30ff mem 0xf0300000-0xf0300fff irq 19 at device 0.0 on pci5
re0: Reserved 0x1000 bytes for rid 0x18 type 3 at 0xf0300000
re0: MSI count : 2
re0: attempting to allocate 1 MSI vectors (2 supported)
re0: using IRQ 256 for MSI
re0: Using 1 MSI messages
re0: Chip rev. 0x34000000
re0: MAC rev. 0x00000000
miibus0: <MII bus> on re0
re0: bpf attached
re0: Ethernet address: 00:03:0d:a1:a8:19
re0: [MPSAFE]
re0: [FILTER]

Those lines in RELENG_8_0 are the same except IRQ 259
(i kldload if_re after boot).
RELENG_8 is from 2010.05.04 i believe;
had tried with sources as of 2 or 3 weeks earlier - same bug.
No CFLAGS except -mtune=native (i doubt it does the weather).
It doesn't matter if i kldload or just use GENERIC.

How can i test further, except building fresh RELENG_8/i386?
How to use a magic "DDB key" and what to input in there?

p.s. I subscribed only to current_at_ so cc me if needed.
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