for the strx-problem; you could either try to disable other plugins systematically to see which one is causing this. if you find it, I could have a look at how to have that one + strx behave when autoptimized. and it might be interesting to see what information is seen in your browsers error console.
for the characters: disabling tiny mce advanced does not help, you would have to disable it and then create a new post (with strong-tags) and see if the problem is still there.