There is at least one known problem with 0.99pl11 - it's very minor and
will not lead to any real problems, but it's also very easy to fix,
so...
The problem is a one-liner oversight in kernel/fork.c (thanks to TjL for
noticing the symptoms - they aren't easy to see), which is fixed by the
following patch:
In fact, it's probably easiest to "apply" this patch by hand: just
change the "p->tss.fs = KERNEL_DS" in fork.c to "p->tss.fs = USER_DS"
and you should be fine.