Me Too! However, I have just 2 PCs listed, pc & pc2; in my case I believe that it happened because of Amazon's Kindle software update as the directories where Kindle appears have changed. Kindle for PC is in a different place than Kindle for PC 2 & the icons were different.
I tried to have the book sent to Kindle for PC & it never arrived or got lost; did it again to Kindle for PC 2 & got the book. Personally, I liked the old Kindle desktop icon better than the newer/latest version even if it was set for Kindle for PC
& that was how I found out about why the 2 devices for the PC.