By everything I can see in the code, Lesser Mind Blank is properly calculating the duration and taking Spellsword levels into effect.
I'm assuming you're talking about Micus here? At the time you reported this, I calculate the duration should have been 9 RL minutes (5 from Wizard levels and 4 from Spellsword synergies). At present, that duration should be 10 RL minutes. Could you please confirm this.
It's worth asking are you possibly comparing other Turn/Level durations that have had their durations doubled through the use of Extend Spell? As a 5th Level Wizard/10th level Spellsword, Lesser Mind Blank is the top of the spells he can cast, so he could not Extend it as he could with Polymorph Self, which is also a Turn/Level spell.
Please confirm we're talking about the correct character.