Why is em nic generating interrupts?

Hello, everyone!

I've got a [uniprocessor 5.1-RELEASE] router machine with fxp and em nics.
I've built my kernel with the following included:

options         DEVICE_POLLING
options         HZ=2500

and enabled polling in /etc/sysctl.conf.

Having looked through a vmstat -i output I see
that the em card is generating interrupts, although
they should be disabled (as I see in em's source code).

interrupt                     total       rate
stray irq0                        1          0
stray irq6                        1          0
npx0 irq13                        1          0
ata0 irq14                     2339          0
em0 irq10                    421457        155
fxp0 irq5                         2          0
atkbd0 irq1                    3326          1
clk irq0                    6778872       2500
rtc irq8                     346899        127
Total                       7552898       2786

What's happening? Is polling working in my case?
If yes, why is vmstat showing interrupts? I see clearly,
that fxp's counter doesn't increase, and em's is constantly growing.

Is there anyone who knows for sure that em's polling works?

Thanks in advance to anyone for an idea!
Please also CC: me as I'm not subscribed.

P.S. I've posted this question to questions_at_, but so far
the question is still open. So if someone finds this post familiar,
please just ignore it.
--
Best wishes,
[mike_at_tric.tomsk.gov.ru].