wd1040 - not too sure how modern you are looking at when you talk about Chinese coinage. If you are talking about the last 100 years, a fair bit of my Xinjiang coins have serious die rotation error. Whoever was working probably never looked when they were striking.
Here's one bizarre 10 cash coin if you missed it:
In coin orientation which is strange as all other Chinese coins I have are in medal orientation. This coin is overstruck over 1895 5 fun and is a mule of Chekiang and Hupeh province dies!
I think I picked up another bizarre error coin on the net but let's see until it arrives.
That aside, here's another Soviet error coin:
Russia 1988 1 ruble, novodel of the Fredrik Engels ruble. Now this is a SERIOUS ERROR. The year is supposed to be 1985, but for some BIZARRE reason, it is noted as 1983!! Noted by Rylov-Sobolin as scarce and is quoted as 200USD back in 1994!
At one stage, this error coin was sold for over 2000USD in one of Gorny auction. I still think it's too high.
My partial coin collection http://www.omnicoin.com/collection/gxseries
My numismatics articles and collection: http://www.gxseries.com/numis/numis_index.htm
Regularly updated at least once a month.