I had that same problem with the most recent port of netBSD that I have 
yet to get it up and running on my SS1+.  I believe someone said that 
using an older version, something along the lines of 1.5.x I think, 
would fix the problem.  On my machine, I installed completely from cd, 
of what looked like a successful install, and then I could never boot.  
Some fatal error would be thrown with some garbage about a "cache flush" 
problem on the HD.
-Andy

Andy Ball wrote:

>Hello Jukka,
>
>  JM> Well, if you manage to install it, it still won't work
>    > too well, due to the cache flush problem of those old
>    > Sparcs.  :-(
>
>I have heard about "mmu problems with sun4c", is that the
>same thing you're referring to?  I've been told that there's
>a work-around in NetBSD/sparc that, although not ideal,
>enables it to run.
>
>How severe is the problem?  I won't try real-time 3d walk-
>throughs or even X on this 25 MHz machine.  That said, I
>suppose with a slower system any dent in performance might
>be more noticeable.  :-/
>
>- Andy Ball
>  
>