Redstone wire powered via redstone comparators (or any block that can provide an output of <15 signal strength, such as weighted pressure plates or trapped chests) that are themselves powered with a signal strength <15 have an odd effect where blocks that should be powered via a strongly powered block under the redstone wire with a signal strength of 1 are not powered if redstone wire is placed on top of them (the redstone wire on top of them has a signal strength of 0, so it looks like the blocks think they should be unpowered, and ignore the strongly-powered block adjacent to them).

Steps to reproduce

1. Construct the build shown in the screenshot "Without redstone dust.png". Notice how the redstone lamps at the end are powered, as they should be.
2. Place redstone wire on top of the last lamps. Notice how, like in "With redstone dust.png", the redstone lamp turns off, because it thinks it should be unpowered. This happens only in the case where the comparator output level is <15; when its output level is 15, the lamp remains on.

Original description

In the attachment, you can see that even though all redstone lines have the same signal strength, only the one that isn't powered by a comparator turns on the lamp on its right. If you remove the unpowered redstone on top of those lamps, they all become lit.