My understanding of this might be incorrect, but I'll put it here anyway.

I have a weapon which slows opponents on hit. Although I rarely (5-10% of the time at best) see enemies even making a saving throw, much less getting slowed.

It seemed to work well the first few battles I fought last night, but then became very sporadic. I have tested all sorts of monsters, and also some PvP sparring and I don't see a pattern except that it didn't work in the limited PvP trial.

Is this bugged?

It is probably an OnHit: percentage Slow (save to negate) rather than OnHit: Slow (save to negate). However, you could easily be experiencing a lag issue -- this seems like one of the places it would occur.

OnHit:Slow only applies with a % chance per hit specified, I think?

OnHitCastSpell:Slow would always be applied.

That's not count saves. This is also just a wild guess based on what Snoteye said.

Okay, based on your comments I exported and took a closer look at things in another module. You are correct, there is a % chance that the effect is applied, actually this is the percentage stated when the item is examined. In my case its something like:

On Hit: Slow DC=14 25%/ 3 rounds

I think the % chance and duration are coupled, but that is irrelevant here.

I guess its hard to say if I'm really getting about 25% or the lower numbers I originally suggested. And sometimes the effect applies on the killing blow. Unless lag is a factor, I guess this isn't something that really has to do specifically with efu.

The duration is tied to the percentage. The lower the percentage, the higher the duration.

My understanding of it:

Everytime you make a successful strike with the weapon, there is a 25% chance that the weapon attempts to slow your opponent.

THEN your opponent makes a saving throw DC 14.

Example 1:

You hit you opponent. You throw D100. You get 54. No slow effect.

Example 2:

You hit you opponent. You throw D100. You get 21. Opponent throws a save. They get a 15. No slow effect.

Example 3:

You hit you opponent. You throw D100. You get 7. Opponent throws a save. They get a 6. They are slowed for 3 rounds.

Generally with the fact that you have to hit, to get an onhit, and then for them to fail a DC as well....you're lucky if onhit goes off 1-5% of your attacks.