Browser information:
Google Chrome. I try it in two different computers, both with Version 34.0.1847.116.
Steps to reproduce:
When you go to your user profile, then to the responses tab, then to comments, and then you select the text of a comment it would look as the Image 1 shows.
Site information:
I have only test it on Stackoverflow.com
The URL would be something like this: http://stackoverflow.com/users/<user-id-here>?tab=responses&sort=comments
Image1:
.comments {... padding-bottom: 10px;...}
is the culprit here...