By default, you have a 1 in 6 chance of getting a specific type of item. The type charm makes that specific type have double the odds, so now you have a 2 in 7 chance of getting that item, and a 5 in 7 chance of getting any other item. Put another way, you now have a 28.6% chance of getting the specific item type you want.

The probability of your event occurring is therefore (1 - 0.286)^7 ~= 9.5%. So roughly one in ten times that you create 7 items, you won't get the boosted one. I wouldn't consider that indicative of anything being broken.

Wait, shouldn't the new odds be 1/3?  I don't math good

Not quite, because then the sum would exceed the divisor. By default each item type is 1/6 chance, IE the sum of the 6 is 6/6 = 100%. If you made the charm cause the item type to become 1/3 (IE 2/6), the sum would be 2/6 + (1/6)*5 = 7/6.

I think you are correct, but who knows what plarium did.  If it is truly 2x chance, it should be 1/3 of that type and 2/15 for each of the others.  This is the only thing that seems logical mathematically.

Hm. Suppose that works as well. Wonder which one they use.

In my reckoning, you have on normal events 6 possible results equally distributed. So the chances to get a specific item is 1/6. 

Now it would be interesting, how plarium handles the situation. 

If they actually stil calculate only 6 possible results being available, your logic is sound as they change the equal distribution of the results to a weighted distribution which leads to your number of 1/3 and 5 times 2/15.  This would fit with doubling the chances. (Unfortunately, I do not have the impression that the charms are that effective)

If on the other hand Plarium is adding another possible result while keeping an even distribution, we now have 7 possible results with 2 of them being the results enhanced by the charm. So we get 2/7 and 5 times 1/7 chance to get a specific type. Even so, Plarium is telling the truth that the charm provides a x2 chance...they are just omitting the addition of *in comparison to other results*,

Your logic would actually make the charms more effective. Do we trust Plarium to give players more control over RNG than needed?

From my admittedly basic understanding in programming, I can imagine that the solution with 7 possible results is much easier to implement. Something like

If *charm type* used add *charm.type* to Array.possible.result

Please do not judge upon the syntax of the line above, it should just give the idea of the simplicity of programming how I would imagine it.

If using your logic, you must implent different percentages for the results to happen and need a table to assign the new percentages for the possible results because you are not using an equal distribution anymore. 

Perhaps I am wrong but I would suspect Plarium to take the easy route and just add to the possible results and not actually shifting the weight.