While trying a new kernel I found that,
wether gtkam segfaults on macppc depends on the kernel.
On the identical setup just rebooting with a different
kernel version

it works on 2.1 RC3 
# uname -a
NetBSD ibook 2.1_RC3 NetBSD 2.1_RC3 (IBOOK) #7: Wed Aug 31 22:39:46 CEST
2005  rudi@ibook:/mnt/netbsd-2.0/src/sys/arch/macppc/compile/IBOOK
macppc 

while it fails on 2.99.15 as previously described in the PR
$ uname -a
NetBSD ibook 2.99.15 NetBSD 2.99.15 (IBOOK) #7: Mon Jul  4 23:40:38 CEST
2005  rudi@ibook:/mnt/netbsd-current/src/sys/arch/macppc/compile/IBOOK
macppc 


Unfortunately on 2.1 RC3 Mozilla exhibits the screen update problem
-horizontal lines when scrolling down- so I will have to switch between
the two kernel versions.

rudi