Addendum: I had a quick look at the options of Internet Explorer and got my hopes up when I stumbled upon the option "Load sites and content in the background to improve performance" but this option does not seem to have anything to do with the tab-caching thing. So this option is ruled out.
I apologize in advance if this is the wrong forum to ask this question. I just noticed something while inspecting IE11 with a tool called "spy++" (don't be alarmed by the name, it's a standard tool provided by Microsoft) and I wondered if someone could drop me a hint on what this new (?) feature...