Hard to capture this one in the discussion title, but here's the explanation: if you create an ability in the character sheet, and click the roll button, it rolls as expected (and with 3D dice active, it shows the dice properly). If you then edit the roll, save changes, and reopen the character sheet to hit the button, it doubles the roll. So for instance, I set up this ability:
Melee: /roll 3d6k2
I save it, and click the roll button, and 3 dice appear and it calculates the answer and everything. If I then edit that ability, and then click the button again, 6 dice appear on the screen (although it calculates the result twice -- so it's not rolling 6d6k2, it's rolling 3d6k2 and 3d6k2 and putting the results in chat). I can reproduce this every time:
1. Create an ability on a character sheet. Could be anything, but I tested with both 3d6k2 and 2d6 rolls.
2. Save the ability, save the character, and open the sheet again after it closes (incidentally, i second the suggestion that saving changes to a character sheet should not close it!)
3. Click the roll button. Roll should execute as expected.
4. Edit the character sheet, and edit the ability. You don't have to change it, just open it for editing and then save the ability again by clicking on the checkmark.
5. Save the character sheet, and after it closes reopen it.
6. Click the roll button by the ability. The roll is doubled (double the dice appear, and two separate results are printed in chat).
OS: Windows 7 32-bit
Browser: Chrome 23.0.1271.97 m, 3D enabled