I experience the exact same issue. If you open the console, you should see Webkit2 WebProcess crash (Dispatch queue: com.apple.main-thread) each time the tabs are unexpetedly refreshed. This is a really annoying bug in effect and disabling Java doesn't look to change anything.
I could determine when it happens for me (reproducible anytime):
• an OTF font-face CSS directive
• a select form element
• each time I click on such an element, the Webkit2 WebProcess crashes…
Be aware that this bug may prevent your users to use forms if they use Safari 5.1.
The only solution I found to get rid of this bug on one website of mine consists in getting rid of .eot font-face directive. But anytime you will visit a website with such fonts, you may get this bug that crashes all opened tabs and you won't be able to submit any form whenever it includes a select box. Since all tabs are getting reloaded, it can make your computer really slow if you had many tabs opened.
This is the worst bug I ever could experience with Safari, I hope they'll fix it right away.