I've had this occur many times before when cloning data on drives, but have just worked out what actually triggers the bug;

if a folder tree being copied by explorer contains a shortcut created by another system, that would not be valid on the current 8.1 system, upon explorer hitting said shortcut either the underlying COM Surrogate (dllhost) or the explorer process itself will get caught in an infinite task thread loop. While everything still responds correctly, the copy window will be permanently stuck on attempting to copy the shortcut file, you cant pause, cancel or close the window and must terminate the COM Surrogate instance for it to bail.

Code-wise I'd say it's attempting to read the shortcut as a folder, and as such then gets caught in retrying. Also note that either of the process instances will consume an entire logical CPU thread due to being stuck without a timed sleep.

- windows 8.1 pro x64 in use at times of bug occurring, managing data on drives from vista (32bit), 7 (64bit) and 8/8.1 (64bit pro) systems.

• Edited by Paul17041993 4 hours 22 minutes ago