Sorry that happened to you. If you have a different browser on your iPhone (such as Mercury, Dolphin, etc.), did you try it on of those, too? After opening a lot of apps in my 4S and switching around, I was able to get the non-refresh consistently in Safari and Mercury. Wondering what may be different here... possibly the number of open browsers you have going are a factor? Maybe if the memory get strained badly enough, the iOS will kill the 'Define' screen even if the feature is coded in such a way as to make it partial to maintaining it for the sake of the user experience.
I gather, maybe incorrectly, from your user ID that you work for Apple. If it's possible, could you refer the inquiry to the development team that is most likely to have coded the 'Copy | Define' pop-up feature? I am thinking that if that pop-up acts as a modal dialog that can be killed at iOS's discretion if memory constraints get too painful, then there is already logic in place to detect that condition. Adding an option to the Settings that indicates that the user would like to be asked when this condition arises if they want to clear the in-memory browser cache to release memory so another app can be run, or cancel further attempts to open more apps until the browser is closed, would be nice. I understand that Apple wants the iPhone to be a "just pick it up and use it" kind of device and for the most part, it is. However when it gets to sacrificing the user experience in the process and making the user feel frustrated (and they don't really understand why), the maker of the product is in essence undermining their own goal: ease-of-use is cancelled out by apparent limitations or faults that appear to be entirely avoidable that inhibit the function of the product. Thus ease-of-use in fact becomes not-easy-to-use.
Put another way: I have no real complaints about the iPhone except this one annoying thing that is presented by any browser employed by the user. Surely *something* can be done to put the decision into the hands of the user rather than force him or her to wait while browser windows re-load seemingly unnecessarily. It's understood that memory in an iPhone cannot be limitless, but letting the user know this and putting the decision of how to handle things when the limitations are reached would I am sure give the user a better sense of control over the device's behavior as well as remove this particular recurring complaint from the gripe-list.