Firefox Mobile renders it well for me, are you sure that the comment is not rendered as it should be (with garbage from line 1 overflowing over line 2)?

I thought the owerflow should be "well behaved" (in terms of correct layout/vertical space)?

Is it correct to have "overhang" into the line below? Isn't it a case of incorrect layout?

I think it is correct, as surprising as it can be. See this famous stack overflow answer for instance: https://stackoverflow.com/a/1732454