Feels like this patch broke the fly spell. Drinking a potion of fly does not change the movement (from 6 to 12) nor does it enable pathing other than normal walking, no matter if the shift key is used or the change elevation is toggled on using the elevation button on the map icon.
For what it's worth, I've used the fly spell two or three days in the academic's background quest. I cast the fly spell in the Caer Lem outpost to get to the entrance of the Timarian tower. The spell did indeed change movement and enabled other / more paths for the character upon that the spell was cast. This also was true inside the tower. The character did not need to jump and do athletics check as characters would normally have to do, he just hovered over from one ledge to another platform.
Seemed to work as expected for me. Game version is 1.1.8, too.
"From then on, when anything went wrong with a computer, we said it had bugs in it." - Grace Murray Hopper
Can confirm, I have the same issue. I drink the potion on Caer Lem in order to fly up to the tower and it doesn't work. I change the altitude with either shift or the compass and it won't allow me to fly up. Moving to another position just uses the regular pathing with the character floating.
I tried both the spell as casted by a sorcerer and the Potion of Fly. It seems the Fly the spell works as intended, but the fly effect granted by the potion is broken (can't change altitude, can't find path, etc.).
According to the patch notes for the 1.1.11 hotfix the fly potion should now work as intended again.
"From then on, when anything went wrong with a computer, we said it had bugs in it." - Grace Murray Hopper