As a Celtic fan, I probably would have done the same. The penalty was really really soft and I felt like they (celtic) were diving quite a bit from the start, but maybe that was because I was watching the match with a Rangers fan :P Not exactly the same intensity I've witnessed in other matches, hopefully it's just fatigue but they're not doing that fantastically well in the SPL either so not sure if they really should be this fatigued just from the addition of European matches.
Typical Celtic though, leaving it to the last match and still not entirely within their control with benfica being able to throw a spanner in the works. Was half expecting Celtic to score the winning goal in the dying seconds of the game just to keep the suspense going lol.