Hi Keithw, 

There are no known issues with the C 8.1 and the Target Weld function. Can you upload screen grab of what your are trying to weld? 

Just as a process check, all shapes need to be in the same vertex 'instance' meaning that if you have to different vertex objects when you look in your Scene Browser, they will not weld. Both shapes will need to be in the same vertex object.

Mark