Slime block duplication glitch still exists in 1.8. I built an exact replica of the slime block elevator given in the link below but I cannot use it because as the platform moves up or down the slime blocks duplicate making it impossible to use for the next time.
This glitch existed in pre-release versions and I hoped it would be fixed in the official 1.8 release however I am still getting the same problem.
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Please provide more information and Screenshots of your setup.