Can confirm that this is still an issue as of 1.2.3.
Cheats are not necessary for this bug to occur.
Hopefully this isn't redundant information but I wanted to add some clarification from my own findings:
This issue affects any redstone circuit that is powered on/off by a switch or redstone clock and does not apply to just redstone lamps (for example: a simple pulsing circuit to dispense "garbage" into lava using two repeaters on 4 ticks each still lags).
As the OP claims, this applies ONLY to circuits being powered OFF.
This applies to both singleplayer AND multiplayer servers (Vanilla and Spigot alike).
Java versions as early as v1.8.0_25 and as recent as v1.8.0_77 are affected.
This DOES produce a momentary frame spike, dropping as low as 30fps from 120fps.
I hope this affords a bit more useful information and look forward to a fix.
Can confirm that this is still an issue as of 1.2.5, well over a year later.