Same SKU but different ID’s on product variations

I use a lot of products with variations and i also use “WooCommerce Stock Manager” (this is where this makes it a problem). It seems that i have products using the same SKU but with different ID’s. When this occures i cannot use “WooCommerce Stock Manager” and save any changes and i cannot actually see this products anywhere else. I looks like it’s a duplicate without a permalink attached to it. It’s like a “ghost” product.
See a example here: https://www.dropbox.com/s/r9z2s0kb9gh9x5v/Stockmanager.PNG?dl=0
I am not a WordPress expert so i need a bit of help here.