Duplicates in supply orders - versions 13.*

Hi, from one day when I try to insert a supply order for items that have multiple prices (for instance for a quantity of 1 and for quantity of 5) what I get is a duplicate of my items in the order (i.e. if I had 4 prices I got 4 rows of product) and if I try to delete one of them I found all those orders cleaned.
The strange thing is that if I start a “clean” dolibarr installation I do not get this strange thing.
Upgrade to version 13.04 changelog states that “FIX same thing on supplier orders”, I suppose referring to this problem, but, after upgrading, it is still there.
Unfortunately I cannot reproduce the facts chain that leads to this error, while still investigating on it.
The error appeared the first time after an upgrate to 13.* from 12.* but I am not so sure that it was absent on 12.5
By the way I am using BOM modules, still before the appearing of the error.
Thank you all

Hi, this strange behaviour is still here with version 14.03.
The only way to let ignore this seems to set a different SKU when inserting a new price from supplier (i.e. I can have a sku 001 when I fix the price for the first quantity, then, for the same product I bought, I have to set a sku 001-b for a second quantity, i.e. I have to add a differentiation tag “-b” that is not present in the real sku of the supplier).
Any guess about it? Thank you all