Said legacy hardware (namely, anything <= K3, with the K4 in between), doesn't support this hack anyway, and ignore just means that: "ignore", not "horribly implode in fun and interesting ways"
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Also, it doesn't really has anything to do with the full-screen thing anyway, that's just to request a flash, which is necessary because the screen content may not have changed, so a non-flashing update will most likely not do anything.