Hi Dima, thanks for raising this. To clarify both of the rows being imported are Variations you are merging changes to or different Product Types? If you can raise this as a Support ticket you can attach a sample import file for me to reproduce and get this fixed.
Re: the duplicate checking we do a few different checks for duplicates, first checking the Product ID, then Product Name and finally SKU detail, if all of those fail and we are importing a new Product only then that Product gets generated, if we are merging and all of those checks fail we do not merge the Product changes. I’ll need to look at how we handle the Product Name column for Variations when merging as this seems to be where you have run into trouble. Happy to look at it with you further as well as other topics that I’m responding to now 🙂