Thanks very much for that extremely thorough explanation Rezzahan.

If this had happened to me, I would've likewise posted it as a bug. The whole "excess of 1 deathtouch damage" is very counter-intuitive, but I understand why they implemented it this way.

It took a few re-readings of rules 120.4a and 702.2 to fully grasp the interaction.

Trample plus deathtouch gets trough any blocker with just one point of damage assigned. That blocker can be indestructible, can have damage prevention on it, or whatever, it does not matter. Damage assignment does not take any of that into account. But it does take into acount deathtouch. And with trample, any damage that is not assigned to the blockers can trample over.

In your particular scenario, you even had an out. You just had to assign BOTH of your indestructible creatures as blockers, which would then have absorbed both assigned damage in the first combat damage step, and then would have to have been assigned that damage again in the second combat damage step, thus absorbing all of it, and you not getting any poison counters.

EDIT: Small correction on the second part. Kotis would have lethal damage marked from the first combat damage step, so would not require any additional damage to trample over in the second combat damage step. Still, you would only have taken 2 poison counters, not 4, in that combat and survived.