Reoccurring Visitors with just one Visit?

Hi, I just started tracking and found something odd,

I got 22 Reoccurring visitors in the logs but out of these 22 only 5 visited my site before (according to the visitor log).
I found in the logs of the 17 non reoccurring visitors that they spend xx s on my site viewing xx pages in 1 Visit.

Any idea why this is happening ?