A new Product Change Notification (PCN) bulletin from Intel confirms the current Lynx Point 8-series and C220 chipsets for Haswell have a bug that causes USB 3.0 devices to disappear after entering S3 standby mode. The issue has been fixed in stepping C2, this updated chipset will start sampling on April 19th but won't hit the market until late July. Affected chipsets include the Q87, Q85, H87, Z87, B85 (desktop chipsets), C222, C224, C226 (workstation/server chipsets), QM87, HM87, and HM86 (mobile chipsets).
Full details can be read at BSN.
According to the PCN the new stepping will be sampled to customers starting April 19th. Final product will be available starting July 15th. Intel also makes clear that customers must be ready to receive the new stepping by July 31st. In other words, this means by then the old stepping will be phased out and gradually replaced by the new one. Due to the minor change needed to fix the problem, Intel doesn't expect a major impact on customers. The new stepping is basically a drop in replacement.
While an official release date for Haswell hasn't been given yet, Intel is expected to introduce the new chip before the availability of the new chipset stepping. Reportedly Intel let customers sign an agreement to acknowledge the presence of the bug if they wanted to obtain Haswell APUs for launch. The bug in question causes nuisances like USB devices to disappear after entering standby. Detachable devices would have to be reconnected to be found again.