[Snake]

Just adding to what Sderg posted:
Basically hit them with a Solar Lance to apply the debuff. Then Sear and throw another lance when the first one is about to explode. It will apply two 'Solar Lance's on the enemy. Then something like this happens when the Solar Lance's explosion proc.

Jokes aside, what I think that might be causing the bug is that the game will use the second lance's duration as valid, after downing the first one to 0 while not deleting the debuff, and continue sapping duration from the first one which is already 0, and since you can't -1 a zero, welp. Solar Lance is too much of an OP Ashe skill for us mortals to use.