Question about vSummon Skellytrons

Hello everyone,
last night I managed to obtain finally the Bones of Ullr to have 9 zombies, therefore my minion count is as follow:

- 9 zombies
- 2 spectres
- 12 skeletons
- 1 totem (is a minion?)

and the Vall's Summon Skeletron gem with 38 additional minions.

Up to that, with simple math, I was sure to achieve the 60 minions achievement (Behold my army) easily ( 9 + 2 + 12 + 38 = 61) but the Vall gem failed me!

Even if the tooltip say that it summon 38 minions it does not summon more than 32, there is a bug in the interface or I'm missing something?

thank you!

Edit:

here a screenshot with the tooltip

http://steamcommunity.com/sharedfiles/filedetails/?id=387712685

Vaal summon skeletons has the upper minion limit like regular skeleton gem, and it also has the number of skeletons you get per cast, again like normal skeleton gem. If you have no 'extra skeletons' mods it will summon a number of minions to match the upper limit, but if you do have such mods it will summon less.

So, you need to cast vaal skeletons multiple times, for that you can socket multiple vaal skeleton gems or just use spell echo.

Or, if you just want the achievement you can get it easily with dominating blow or summon raging spirits.

I got the achievement (thank you for the spell echo tip, didn't know it could work), but still I don't understand why it summon 32 minions instead of the 38

I already told you, you had +6 to skeleton upper limit from tree and gear. A level 16 gem normally summons 32 skeletons out of 32, with your bonuses it summoned 32 out of 38, working as intended.