It looks like the debuff overwriting bug has been fixed. Sniper Shot now properly overwrites Outrage and persistently increases damage, and the second Outrage after Sniper Shot now misses as it should. It's unclear how this affects other anomalies such as Regen overwriting.
The most immediate effects of this are that Auto-skill with Mordred and Sniper Shot will work better, and Raids won't be permanently gimped by new players using weak debuffs early in the fight and blocking veterans from applying the stronger versions. That'll make Ragnarok Raids much easier.
I've updated the Buff and Debuff Stacking section of my guide accordingly.
A video of my 2nd test will be made available here shortly.