User blog comment:Xilinoc/Ch. 552 - The Fundamental Virulence/@comment-5551986-20131008165851/@comment-11051098-20131010084146

The Visored were captains and lieutenants before the Hollowfication incident, so their Zanpakutôs existed first. But seeing as they have Hollow-like powers due to that incident, their Bankais should be impossible to steal, just like Ichigo's was (and I suppose still is).

Or maybe their Bankais could be stolen, but due to the Hollow-affection, immediately cause injure to the Sternritter who stole one and activated it, deeming it useless to the Sternritter.