For some reason, sometimes when I copy/paste a symbol or a group of symbols, it creates a new symbol in the symbol page which creates a huge mess and I end up having the same symbol many times. I disabled the renaming feature so they all have the same name. How can I avoid this? 

Thank you

UPDATE - THIS WAS A BUG AND IS NOW FIXED in 43.2 :
"Fixes a bug where copying and pasting Symbol instances could duplicate their master"