i don't think Luke felt any joy in choking those 2 gammoreans. he just did that to get them out of his way. If he was planning to bust everyone out, he could have just strode in the palace with his lightsaber and killed everyone.
and do you remember the Mace-Sidious duel? sidious' lightning was arcing back on himself off of Mace's saber. the same thing might have happened if you really stick by Yoda doing something to Sidious, but i say he was just surprised that Yoda could survive under the assault.
Duct Tape is ALWAYS the answer