On my Fighter, after going back to town, entering the Inn, choosing my fighter (party position 1), chose the stables, and he levelled up. Once the levelup screen appeared, I had 3 points to spend. I intended to mouse over AGILITY and then use the right arrow to assign them, but I accidentally moused over STR pressed the left arrow... and much to my surprise, my strength went DOWN below its original value of 18 (and the ability score text turned red, and a minus (-) symbol appeared next to it). I decided to press left arrow a few more times, and the score kept going down. All the way down to 3. I tested a bit more and it seems this is only possible if the original value of a score is 18... but you can use left arrow to drop an 18 down to a 3. The available points will be unaffected (even after lowering my 18 STR down to 3, I still only 3 points to spend). It seems you can use the right arrow to raise the score back up - but this is likely to confuse people.