Safari acting weird

Hey you guys (and gals),

I've been looking for a simular topic, but the problem is so strange to define it, that I could not find any...

I'll try to explain, so here goes:

I've been browsing for a while now with Safari 6 as my standard browser, but since my last software update (that even didn't involve Safari) it's having his own way.

As a webdesigner I view a lot of websites over a day, but sometimes when I click a link or a button on one website, it preforms the action on a random website I viewed before.

For instance:

If I'm on site A (www.example-a.com) I see site A and it works as it should, but sometimes (it's randomly, I don't actually know how to reproduce this issue) when I click a link or (press a button to) submit a form, it navigates to website B (www.example-b.com) to preform the action (eg. logging in, going to a certain page, ...).

Do you know a fix for this situation?

Many thanks in advance!