Problems with revealing areas for Fog of War

When trying to reveal areas with Fog of War enabled, if I get too close to the edge of the screen while dragging the box, I'm getting a problem where it suddenly reveals the entire map (instead of only revealing area of the box I was drawing). Then, if I go to page settings, turn off Fog and save, then turn on Fog again and save... the map "fixes itself", showing the Fog the way I intended it to look. I'm also getting some similar weird revealing bugs when trying to re-hide areas with the tool. Kinda hard to explain, so I'm attaching some pics. #1 shows after the glitch, where only a box area of the map should be showing, but instead is showing the entire screen. #2 shows what it looks like after I turn Fog off and back on again. It appears this bug is only happening from the GM point of view. I logged into my campain using a test player, and the glitchy reveals did not show up on their map view. GM account using Mac OS X 10.5.8 running Firefox 12.0 Test player account on the same computer, running Google Chrome 18.0

Update: This bug now seems to be happening within this campaign whether or not I'm dragging the box near the edge of the map. In a different test campaign, I wasn't having this problem... it only started in this campaign when I drew a box that went right to the edge of the upper left corner of the screen.