That's the announced policy... But I know of two individuals who are back, full time regular, after being laid off. Depends on how desperate they get... They do allow exceptions, that is.
"They don't want to waste the money that they invested in your layoff" is a paraphrase of "why", according to them. They don't want to "invest" in giving you your go-away money once, and then end up doing it again. Yet an easier "fix" to this "problem" is much easier... If you are back time #2, just under-pay your pay rate for a few months or quarters, till you are back up to fair-and-square (paid back, paid off in full for previous go-away money), and then jack your pay rate back to normal for your job. Am I a finance genius, or what?!!?
My personal opinion here is that the REAL reason why they do this is, so that they "can't find anyone anywhere" to do the job, so they just MUST hire more H-1B immigrant workers! To save more money for Meg, of course...
Yes, it's stupid... Perhaps also evil! For one thing, it encourages the laid-off, to sue... Why NOT sue, if there is nothing to lose?