Why and HOW can a track number show under two sales to different states? HELP!

[cosi-shopper]

OK, I make boo-boos sometimes and sometimes a printer dies and I have to go print a label somewhere else. That said, none of that happened with this issue; 

I have two items sold, printed the labels without any kind of glitch or delay, shipped them off = two different names, two different states.  

THEY SOLD TWO DAYS APART;
*OCT 7 item, label printed Oct. 7th.
*OCT 9 item, label printed Oct. 10th

Now, on my SOLD page I see one of the items has it's USPS tracking number as usual PLUS the tracking number of the previous item. There is a drop-down menu and I can check history for each tracking #. Whoa!!! What the...? 
I don't even see how the # could show for 2 items, I thought, pretty sure, eBay has a fail-safe for that.

So, one is showing as delivered, whew, but the other states "arriving on time". 
I guess I won't know if the second one arrives safely until after the Columbus Holiday. 

[cosi-shopper]

I don't hand-enter tracking numbers, I buy eBay labels and numbers are automatically entered.

[martoutlet]

i know you can't add the same # for 2 different buyers,at least the first #.

you can remove the # that doesn't belong to buyer.

click on add tracking and clear # and USPS.