I suspect it is more of a memory and resource saving method then a bug.
I think there are several issues being discussed here, or at least by psylichon.
The issue of not keeping the cache of open pages is one thing, probably memory related. This is not necessarily a bug.
But another issue, and this is most definitely a bug, is Mobile Safari's (annoying) behavior of "forgetting" the active page should you leave it due to a open-in-new-tab link. The expected behavior after closing the newly opened tab and returning to the original tab is to be
right where you left it. But that is often not the case. I think this is what psylichon was referring to. I do the work-around of quickly returning to the source tab (while the new tab is still loading) but I don't remember to do it all the time, and sometimes it doesn't work (in which case I use the History bookmark to get back to the page I had been on).
A related bug (if you will) is that Safari too easily forgets the back button. I call this a bug since the pages the back button would have pointed to are still in the History bookmark.
As for the number of tabs, I often have 6+ open all of the time, and hit the 8 tab limit weekly. I wouldn't mind the 8 tab limit being increased, or perhaps a way to have two copies of Safari loaded/saved at a time (kinda like having multiple browser windows open on your PC, each with multiple tabs loaded). Yes, this is a mobile phone but I've gotten used to using it for many Websites that I would have--before the iphone--only viewed from a "true" computer (indeed a can't wait for Firefox to have some sort of "click at the top to go to the top" type of control, like the iPhone has

).
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Mike