Though now fixed, the patch notes, as highlighted by Kirk Patrick, state that no one had figured this out before.

Developers’ note: The absorb shield from Val’anyr was always intended to have a cap of 20,000 health, but there was a typo in the spell script in original Wrath of the Lich King version 3.3.5. The script was set the absorb amount to 200,000! This was never noticed by players in original Wrath.

Sometimes bugs are obvious; others, however, are rare enough to not warrant much attention. While you’d expect a bug that juiced an item’s stats as much as 10 times would’ve been spotted and documented by someone at some point, Val’anyr’s legend is a tale that reminds us just how complicated games can be and how easy it is to overlook typos and other accidents. So if you secretly knew that you could absorb 200,000 points of damage instead of the intended 20,000, and never told anyone, well the party’s over; it’s now been fixed.