Why is the clipboard content pasted when i type an @?

[out_of_blue]

Recently when i was searching for a text viewer- editor i noticed that if i have something in clipboard it will be pasted when i type an @. It does not happen with all apps though. The problem is there with text editors (I tried Basic Text Editor and NotepadX), but not with World mobile. Also it happened when tried sign in to my Yummly account. When typing my email address i got instead of the @ a nice long url i sent over from my computer before. I found some app in Store called Clipboard Cleanup, it said my clipboard is cleaned, but after closing it, the problem was still there and also my clipboard content. The only way i could fix it was rebooting my phone. Can anyone tell me if this is some OS bug, or some app is causing it or just my phone went crazy? I have a Lumia 950 with Windows 10 mobile and I am not Insider.