Guild Wars 2

I thought that if two sigils of the same type are placed on the same weapon only the first would apply. Is that true in all cases?
Are there exceptions?
If there are exceptions where is that information listed? (Have not found such on the wiki).

Examples
Condition Duration – Agony, Chilling
Permanent Bonus – Accuracy, Force
On Kill – Bloodlust, Corruption
On Critical Hit – Air, Fire
On Weapon Swap – Battle, Energy
On Hit – Fraility, Ice

Thanks

Since the April Feature Patch, all Sigils will stack except under the following cases:

2 of the same Sigil, regardless of Rarity/Type.

Example:
Superior Sigil of Fire + Major Sigil of Fire will not stack. I believe mainhand will proc and offhand will never proc (or if it does, it will be on a shared cooldown, unconfirmed).
Sigil of Fire + Sigil of Air will stack, regardless of the rarity used. The activation chances are calculated individually.

2 on-kill sigils that stack stats will not stack:

Example:
Sigil of Bloodlust and Sigil of Perception will not stack, the mainhand stacking weapon will be applied.
Sigil of Bloodlust and Sigil of Celerity will stack, you will gain one of both stacks per kill.

Last night I played my mesmer who has a Superior sigil of speed on her focus. In the past when she killed something she would get 20 sec of speed. Each additional kill would stack another 20 sec. But last night I was getting almost no speed boons at all.

Has something changed in the last week or so?

Not really, friend was just mentioning the other day that he built up 2m+ of swiftness with that sigil.

My bad. When I looked again the sigil was not in the focus any more. I don’t remember replacing the focus with a new one so not sure how that happened but I placed the sigil into the (new?) focus and everything is fine now. Yeah I got 2 mins+ just this evening. I love that sigil on my mesmer.