I've identified two problems (likely bugs). Both occur using maptool 18.104.22.168 on up-to-date Ubuntu 16.10.
1. When you move a light source which has bright and dim light radii, the light is sometimes (apparently randomly) displayed correctly or at other times the bright light extends to the radius that the dim light was supposed to. This problem didn't occur using maptool 22.214.171.124 on the same OS, so seems to have crept into the code recently.
e.g. Lamp: circle 15 45#000000
2. When you create a light source with a bright light radius of 0, the bright light extends to the map vision limit. This problem also occurs using maptool 126.96.36.199 on the same OS. Possibly relates to this bug: http://forums.rptools.net/viewtopic.php?f=21&t=17859
e.g. Spell - Dancing lights: circle 0 10#000000
If others can confirm, I'll post in the Bug Reports forum.