How to test and reproduce:
Select and allocate random points and preference till 'Gender' to 'Abilities'.
Note your con value, let's define our con value to 
Right-click 'Skills' button and allocate 1 point to dagger, click back, and see the
con value increased by 1.
Doing Step 3 will increase your con value by 1 till it reached the max. value of 25.
NOTE: I'm using mods*, e.g. SCS, etcetera. SCS is a lon long way to install, so I'd let the developers test and reproduce this if this is recurring.