In another topic people sometimes have problems during updates when using certain unzip programs. I always use 7-zip and haven't ran into any issues. But sometimes when people use the default windows extract or some exotic programs they come across update problems. Hangs on different stages of the update. So it isn't always a faulty tf.As a 'last straw' I reformatted the tf card and put zt-update on it again - it worked this time - though I had to start again setting up the apps etc - but at least it isn't bricked anymore.
I suspect my 32gb tf is faulty - I'll be replacing it asap