i actually think that (iirc) it'll make a gesture based on the difference of position between the vkb-showing touch and the vkb-hiding touch* - i've just learned to abuse this instead of bothering to fix it...
touch up-right to show vkb, touch up-left to hide it => gesture right->left.
When drag mode in "Gesture", the gestures seems to trigger easily when not making a actual gesture.
Press a key from vkb (or type a text) then immediately touch the non-vkb area. This will hide vkb and trigger gesture without making a drag.