Searching cPanel reseller ACL on Google shows this thread and a few others.
Judging by other threads it looks like there's a number of the Blesta devs along with other forums members that simply don't understand (or don't want to understand) exactly how WHM/cPanel assign reseller limits and the capability of the API. The ACL's aren't assigned per package, but per account and therefore they have to be assigned in one of the following fashions;
1) Assigned by calling setresellerlimits in the API on account creation (Blesta doesn't do this).
2) Manually through WHM post account creation.
This is a pretty fundamental part of the reseller account creation process, and without this Blesta currently doesn't server those that sell reseller packages very well using the core cPanel module. Comparing the module to WHMCS, ClientExec and free alternatives like BoxBilling I can see that these other systems have nailed this. Why is Blesta missing some really very important functionality? Nothing seems to be happening with it at all.