Cannot copy/paste multiple (6000) files in finder

Hello,

I have 6101 small files in one folder. I want to copy these files to another folder, using finder.

I select all 6101 files. Click "Copy 6101 Items". Then I go to target folder and click "Paste items", only 1580 files are copied, why?

I don't get any warning/error messages.

Best regards

Kari Surakka