Resourcefulness lower than stated on crafting details

[Morphnir-draenor]

I have a few crafting professions and I noticed that resourcefulness seems bugged.

For example I had 2 crafting sessions on blacksmith

1. 204 professions hammers crafted (green ones which require only one alloy)
   I got resourcefulness proc 16 times which is 7%
   at the time I had 25% resourcefulness on crafting details
2. 258 hammers crafted
   proc 21 times which is 8%

On the other hand while crafting on my other alt which is tailor I had materials for 500 pioneer’s cloth cuffs and got resourcefulness proc +/- 28% while having 23% resourcefulness on crafting details

I didnt test other professions for that matter but this seems like a bug

[Lethora-shadowsong]

As far as I know, it works differently on crafts that require a single item to prevent it being too powerful. So, not a bug.

[Griyfman-silvermoon]

If it works like this - please source

Regardless, it remains a bug from our, user, perspective, since we are not informed of that interaction in game in any way.