It seems that movement spells/potions don't effect my Swashbuckler. Is this a bug, or is it supposed to be this way (because I didn't see Free Action in the kit description).
I saved Suldanesellar from destruction, and all I got was this stupid amulet.
Indeed, swashbuckler has not such an ability, therefore his movement rate should be affected by various items/spells/potions. Are you absolutely sure that your PC has no items equipped that grant FreeAction?
The Free Action effect may be bugged and get "stuck" permanently. Check Baldurdash, I believe they have a fix.
[url="http://www.sorcerers.net/Games/BG2/SpellsReference/Main.htm"]Baldur's Gate 2 Spells Reference[/url]: Strategy, tips, tricks, bugs, cheese and corrections to the manual.