Viber Thumbnails automatic saves

[Igor Pajic]

I have a question. Why is Viber saving thumbnails photos of contact img of ppl I never texted or called Viber or my phone. I noticed that there are some thumbnails of some guy a have in contact but never called him or text him, and then I started to check from time to time same for other ppl, What gives deos anyone has the same problem. Tnx