Thanks for link! From that description this seems more like touchpad reporting wrong key presses.

I am interested to check what kind of touchpad my notebook has, but it’s broken at moment. :(

Well I respect that but I found some sites (can post only 1 link into here though bcoz of the commenting system) that suggest some configuration of Opera in order to make the horizontal scroll work, so I guess the problem exists *or at least existed not only for my setup*:
http://en.gentoo-wiki.com/wiki/Synaptics_Touchpad#Opera

I can only suggest trying opera:config (in address bar), searching for scroll and looking through related settings.

Never encountered or heard about such issue in Opera.

Yep, it’s on every site. The horizontal scroll however works on other browsers just fine (ff, ie).

Really not sure what the reason might be… Is that on any site as well? Some sites are coded in the way so that might hinder horizontal scroll.

On my freshly installed win7 I did a clean opera setup.
I have this problem with my two laptops, both use synaptic touchpads, and this problem occurs both on win7 and ubuntu 10.10

You mean missing completely? Works just fine for me (and scroll with wheel is still present and just as awesome).

Had you tried clean reinstall?