I noticed that if you look on a slimeblock through an exploding firework, the slimeblock will disappear, but only for a few seconds till the explosion "aura" is gone.
With friendly greetings,
palex00
Environment
Windows 7, Java 7 Update 67, 32-bit, 4 GB Ram, No mods installed on 1.8.
Stained glass blocks and stained glass panes also have the same issue as the slimeblock