I was contacted yesterday by Apple support yesterday as well (honestly, I was blown away to get a call from them looking for my input on this - kudos Apple!) and I connected my phone to Xcode to extract some logs that I then sent to Apple. I was asked by Apple to trigger a log capture when it happens (press home + either volume button) which can then be sent to Apple for investigation. Good to know they're actively looking at this.
But Solarc, you're at least partially correct. At least for me, if Safari gets more than 2 spaces away from the current app on the multi-task list, the page will refresh every time. I've got a handful of other apps that refresh as well.
However, I think it's not necessarily the sheer # of spaces down on the multi-task list that determines whether it will refresh. I just did some testing on this and I've been able to regularly get Safari to refresh when it's only the second app down from the current app (i.e., it's still partially visible on the multi-task screen, the third app in the multi-task rotation). I think it may have to do with total memory in use by the apps being switched between, especially the amount of memory required by the app being switched to.
For example, I have five apps I've tested with: Safari (with this forum page loaded), a call task app (MobileDay - lists all conference calls for the day), a scripture reader app (essentially like an eReader), iMessages, and the phone app. If I merely switch between the first three apps, selecting the third app each time, Safari will refresh almost every time, but the other two won't. However, if I scroll up and down in App #1, or do other activity like switching tabs; then scroll up and down in App #2 or load new content; by the time I switch to App #3 it will also have a higher tendency to refresh.
However, just now, Safari was App #2 (phone app was #1 - I'm on the phone). I switched from my call back to Safari (after about 4-5 minutes) and it refreshed.
Here are a couple scenarios I just went through:
Scenario 1: Safari, Phone (on a call), Reader app (static, no scrolling)
I was able to switch multiple times (4-5 cycles) between all three without Safari refreshing.
Scenario 2: Safari, Phone (on a call), Reader app (scrolling up/down through multiple screens of text/content, reloading content, etc.)
This is more of a mixed bag. Sometimes the scrolling/activity will trigger a refresh in Safari, sometimes not. The longer I wait inbetween switching back to Safari increases the likelihood that Safari will refresh. The variance is increased by the amount of time you wait (e.g., a 5-minute wait will significantly increase the likelihood of a refresh compared to a 30-second wait).
Scenario 3: Safari, Reader app (static, no scrolling), MobileDay
With these slightly "heavier" apps, Safari would refresh more times than not. The more activity I performed in the other two apps, the more likely it seemed that Safari would be to refresh.
I can play with this some more to see if I can capture a more definite threshold that will trigger the refresh, but this should give you guys something to test with if you want.