I'm not sure if the guy who just posted answered your question, and if he did, then I am probably interpreting the problem wrong, but firstly, what do you mean by the others don't work? Do they not increase STR or do they increase it by too much? The problem I see with this is that it would increase it by too much, unless you first remove the previous mastery level.
This is because calling the common event will run and for each skill will add the STR associated with it. It is an easy fix, but is this your problem?