This has happened more that a few times. Most recently while traveling across the map boundary from o_semos_mountain_n_w2 to 0_semos_plains_n. I allowed the character to travel with no keys pressed and no mouse action, hoping to get a clue from how and where it stopped. It traveled east and stopped about halfway on it's own.
The another time happened in the kobold cave in 0_semos_mountain_n2. Again I was using the cursor keys after having used the mouse to select an autoroute destination previously. The character was traveling south under autoroute when I pressed a cursor key to stop it. It turned to the right instead and collided with a cave wall. The feet were constantly pacing. When I used the up and down cursor keys, it moved those directions but as soon as I released them it turned again to the right and continued to step while stopped at the wall. It wouldn't stop until I pressed the left cursor key. Then it behaved normally.
The OS here in Win7, all updates, on a 1 year old Toshiba laptop using a Celeron CPU. Java installed was Release 6, Update 24 for the first instance. I updated to 30 and then encountered the second instance.
This is similar to an older report ID: 2976302 - http://sourceforge.net/tracker/index.php?func=detail&aid=2976302&group_id=1111&atid=101111