Wires are turning off on world load / not saving state on world save / whatever.
In configurations like (if red_wire == 1 then red_wire = 1) in logic gates, wires turn off on world load, making memory cells, flip-flops, etc based on gates logic pretty much useless in many cases.

BuildCraft version: Works properly in 7.1.23 (1.7.10). Doesn't work (turn off on world load) in 7.99.8.2 (1.11.2), 7.99.15-pre6 (1.12.2) (tested on all three versions).
Singleplayer or multiplayer: Tested only in singleplayer.

Should be fixed in d5cff76

I am sorry, but what is the point of reopening this issue, if this is already fixed in pre7? To close it once .15 will come out?

Yes, we currently only add the label and close issues when doing release.