I wrote:

> Anyway, I'll check more what trigges the problem on my 7248.

Hmm, it looks an old bootloader triggers the we(4) problem.
A kernel loaded by the following version have the problem:
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>> NetBSD/prep BOOT, Revision 1.5
>> (tsutsui@mirage, Tue Apr  6 22:42:26 JST 2004)
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(sorry for too old one)

But the we(4) works fine on the same kernel loaded by the latest loader:
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>> NetBSD/prep BOOT, Revision 1.7
>> (tsutsui@mirage, Sat Jun 10 10:38:59 JST 2006)
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Note I booted kernels via network (pcn0) and
used the same latest nbprep-mkbootimage.
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Izumi Tsutsui