Accessory manufacturer Plugable recently ran a test to see which USB-C hubs and accessories, docking stations, display adapters and cables were compatible with the MacBook Pro 2016. The notebook offers between two and four Thunderbolt 3-enabled USB-C ports depending on configuration, but the site has found that some Thunderbolt 3 DisplayPort and HDMI adapters, along with some USB-C 3 port hubs, are not compatible with the device due to the type of controllers they use.

Based on the results, Apple has chosen to prevent Thunderbolt 3 devices using first-generation Texas Instruments controllers from enumerating and functioning with its latest MacBook Pro lineup. The notebooks are only compatible with devices using second-generation Texas Instruments TPS65983 controllers, including Plugable’s upcoming Power Delivery and Charging dock.

It is unclear why the company has chosen to prevent early adopters of the Thunderbolt 3 standard from using their accessories with the new MacBook Pro lineup, especially since the standard only began shipping in Windows-based devices since December 2015. The incompatible devices include those using Intel’s Alpine Ridge controller or the first-generation Texas Instruments TPS65982 controller.

Whatever the case may be, it will become a sticking point for those who decide to buy the new notebook, despite the number of Thunderbolt 3 early adopters being comparatively small to mainstream adopters. Plugable says that certification of solutions across different device types is still in-progress for the second-generation TI chipset, while all current Thunderbolt 3 cables are compatible as they do not use any controller chips.