Thanks Gold333. I re-posted that paragraph (with some updates/revisions) to the wiki/iOS8/Problems section. I included the youtube video as a reference to the Private mode aspect. Let's keep this up if we can. The text I posted is in quotes at the bottom in case a re-post is necessary.
I just tested it and this security flaw still exists on iOS 8.1.3 on my iPad Air 2. I submitted feedback via a bug report as an 800 character excerpt of the wiki post to (hopefully) keep it on their radar.
As a side note, what about just not switching away from an app when something sensitive is displayed? It will not fix the problem, but with some conscious effort it can at the very least prevent saving screenshots of sensitive information until it is fixed.
Wiki/iOS8/Problems Text:
"As of February 10, 2015, the iOS 8.1.3 release still contains a serious security flaw in cached screenshots created during multitasking. This security flaw has been known publicly to occur since October 5, 2013 and has persisted since iOS 7.0.2<ref>{{cite web|url=https://discussions.apple.com/thread/5413121?start=135&tstart=0}}</ref>. The iOS saves screenshots of all applications upon switching away from them so that when an application is opened it displays the saved screenshot for 2 seconds while the application loads in the background. This iOS feature is to give the illusion of immediate application response. However, due to the screenshots being saved for all screen orientations (3 for the iPhone and 4 for the iPad), users at times momentarily see screenshots that may be months old when loading applications, even browsing history that was performed under Safari's Private mode<ref>{{cite web|url=https://www.youtube.com/watch?v=qPLXJPHfcgE}}</ref>. The problem manifests itself when using an application, switching out, changing orientation, and then switching back to the application. When the application loads, it temporarily displays the screenshot that was saved last time the application was in that particular orientation and switched away from, which is not necessarily what was saved last time the application was used. The temporary screenshots are a security issue because they can show any personal, business, or private data, which presents a significant security risk. This security flaw is not permanently mitigated by clearing out application cache or resetting all settings, as recommended by Apple. Resetting the device only clears screenshots saved prior to the reset, but new screenshots are saved every time an application is switched away from. This security flaw is not application or hardware specific, it is a known and persistent iOS flaw."