Downloaded, integrated to prc_scripts.hak, started module anew with old character... Bladesong Int to AC works with light/thin blades (even without proficiency). Song of Fury also works (it seems it will work with any weapon). Changing maps, swapping weapons and saving character than restarting had no corrupting effect to AC bonus. All quicktesting was done as singleplayer.
I will report when I play some module with this fix and corrected bladesinger character build, if there are any problems.
Thank you for your fast intevention.
P.S.
There might be same trouble with Arcane Duelist chosen weapon, as script wont recognize chosen weapon (rapier/shortsword) in light/thin blade (i.e. wont applie Enhancement bonus). I am not sure it should, but description implies if you have proficiency with those, they count as respectfull "human" weapons for character features.
-Edit-
Testplayed thinblade wielding wizard-bladesinger-eldrichknight character through few modules, all things mathematical work as they should it seems: rapier's criticals, focuses etc... Of notice - both thin and light blades wielded by this character call for "attack increase" and "attack decrease" icons in main hud - as said already, attack numbers in stat window are as they should. This is probably tied to how rapier/short/longsword focuses applie to elven swords.
Also, there is an inconvenience, as standard function for modifieing weapon looks doesnt work for thinblades.
Anyway, while on low levels change from 1d6 of rapier to 1d8 of thinblade is noticeable for low strength character, later when enhancement bonuses go high and elemental damages happen it isnt significant. So using this thinblade over rapier is mostly cosmetic. Also, if rapier compared to lightblade, elven sword turns to be worse - same stats except size been small instead of medium.
This led me to use some "homerulling" and granting elves (Sun Elves in this case) profficiencies with those blades for free (as they get both rapier and longsword for free). 2da is attached.
Also, as gishbuilding got optionless (of full bab full spell) with Eldritch Knight requiring "Martial All" and 3 class limit of NWN program, I used "homerulling" change from "Martial All" to "Martial Any" to get 17/16 gish (if I had to take dip of some class to have Martial All it would be 17/15). 2da is attached.
There realy is a need for some prestige with full bab full spell progression that might be used on top of wizard/bladesinger without cheating:)