I've noticed a difference if I instruct Opera to identify itself as Mozilla 5.0 vs. Opera.
I generally like to keep myself identifying as Opera so I can contribute to its numbers in webmaster reports and such. If people have to identify as Mozilla instead, how are webmasters to know how many of their viewers might actually be using Opera instead.
And to answer your question, with specifics this time, the 2 domain names that I can't tell apart are semtechsolutions.dreamhost.com and semtechsolutions.com. When displayed in the HTML dropdown box, they show up as semtechsoluti...com and semtechsoluti...com respectively so that I can't tell which is which.
No problems though if I change Opera's settings to identify as Mozilla 5.0 instead and then refresh the page. So that's the workaround I have to use, just so you know.