Ah, i see. The change from True to 0.5 signifies desire to "downgrade" the emotion, since in a way it's a change from 1.0 -> 0.5 But because the value is still > 0 the game treats it as Lena having feelings for Ian and acting on them.
PilotLara this could be probably considered a bug, because the game has Lena during the night talk at the beach act in opposite manner to what the player has chosen ("It's just a casual relationship") and asks Ian to "upgrade" to full relationship.
Perhaps the check here
Python:
# LENA LOVE
if lena_ian_love:
$ v12_ian_lena_over = True
should be for
lena_ian_love > 0.5
so in scenario where Lena opted to keep relationship casual the game will handle it as the FWB arrangement it technically still is and the player wants to keep it this way.