Mining an enderchest with a silk touch pickaxe drops both the chest and 8 obsidian

If you mine an enderchest with a silk touch pickaxe it gives you the chest, as intended, but it also gives you 8 obsidian as if you had mined without a silk touch pick. Me and my friend are both able to replicate it consistently.

EDIT: Sorry I was vague in my report, here's some details. This takes place on a realm opened shortly after 1.2 (though there were some world-replacing shenanigans that took place when we were trying to fix some issues, the pick was obtained before these shenanigans took place). The pick is a diamond pick with nothing but silk touch on it (obtained through villager trading I believe). There is no beacon on the server and no potions were involved. Since the realm was opened after Better Together, the pick was, of course, obtained after 1.2.