This problem started cropping up after the introduction of PBR. We have had many reports of this in Firestorm support, and it does repro on the official SL viewer.
The problem generally involves letter/number displays that are scripted to change. Other parts of the object are not affected.
Typically the scripted item will make its texture change, and the texture will rez, blur, rez, over and over, or simply remain in an unreadable, blurry state.
Right clicking the item or putting it into edit mode will often cause the textures to completely rez. Once the item is deselected, it blurs again.