Hmm, poltergeists, fun topic! Here is a hypothesis that could answer your questions…
Off the top, we should remember that IF our true reality (all that there is - ATTI) is data-driven (which I have argued that it is), almost anything is possible. For example, we may have a set of rules that describe forces and mechanics and 99.9% of all reality experiences comply with those rules. This would be necessary and make sense given that our apparent physical reality is programmatic (and therefore malleable) and yet needs to appear “solid” to its “players.” And so, experiments in physics designed to test these rules (e.g. relativistic equations) generally confirm them. Aberrations are either thrown out as anomalous, or don’t tend to appear in experimental laboratory settings. However, they occur rarely in our normal experience (“rarely” again by design, or we would have a different set of rules for normal reality). How might this happen?

Taking a page from Robert Monroe’s “Far Journeys” (which is a similar page in many other bodies of knowledge about how the afterlife works), some people just aren’t ready to die. In Digital Consciousness parlance, instead of fully detaching from their connection to the Reality Learning Lab (aka our apparent physical reality), they retain a connection and continue interacting with it via their consciousness despite there being no corporeal body there representing their existence in the RLL. That “interaction” is just data transfer and may follow a certain set of rules about how a discarnate consciousness can interact with the RLL. Perhaps, for example, the effect of their intent is heavily filtered by context. For example, if you’re alive when you interact with that kettle of water, you are following normal rules of mechanics; your consciousness sends your intent to have your hand turn the knob on the stove to light a fire under the kettle. The consciousness of everybody in the room receives that information and generates the visual impression of that activity. If you are dead in the RLL but your consciousness is still playing around with the RLL (you might or might now be aware of your actual state of being - Monroe generally ran into the type that was not aware), your intent is to create the state of boiling water, which you CAN do because data is infinitely malleable. Perhaps ATTI (the system) allows this periodically and may even favor the rare occurrance of such experiences in contexts where there are people present who tend to believe in such things. Why? So as to reinforce their beliefs? To teach them something new? We can’t be sure because we can only infer the "mind" of ATTI. But, I suspect that if this is the case, it has to be localized; otherwise we would have a whole new paradigm of reality to deal with all of the sudden. Keeping it small and localized (and not subject to broadcast) ensures that there is always mystery - the kind that drives investigation, but not a wholesale shift of belief system. It appears that it may be important to maintain the appearance of a deterministic materialistic reality because otherwise humanity wouldn’t trust RLL, think they are dreaming, and chaos might ensue. ATTI may have evolved to ensure this balance.

That’s my best guess without a whole lot of thinking. :)