When you copy and paste a local variable or a section of the block diagram containing a local variable, the new copy is not the same as the original - it contains an instance of a new local variable rather than an instance of the original local variable, and a new control gets created somewhere matching this new variable name. Doing "Select Item" on the new variable lets you set it back to the original variable's name, but still leaves an orphaned control somewhere on the block diagram.
Is there a way to cause copy and paste of a local variable to create a new instance of the same local variable, rather than creating a new variable?