Tiff files created with GIMP 2.8.6 appear blurry in 1:1 view, while png, bmp and jpg work fine. Tiff compression options don't seem to have any effect. GIMP loads fine those tiffs as gwenview does. Tested on Archlinux i686.
Actually png and bmp seem also affected by this issue.
It seems that zoom quality "Hyper" is causing the issue.