I can just add in that myst portals definitely does not keep a chunk loaded. When I had my delivery system link through the myst world I had to portal over there myself constantly to keep the carts flowing. Same with my lava pump in the nether, it won't do anything unless I'm actually there, despite a myst portal being right next to it.
EVE Online characters:
Daedalus II ex-CEO TOGOA, Daedalus III slave of Daedalus II
Little Molok Asura Engineer
"Trying is the first step towards failiure" - Homer Simpson