Switched-Lighting Woes

This entry discusses several, probably-related issues having to do with lighting weirdness in a world I recently created. First, the venue:

I constructed 1200 m of Powered Rails running straight and level through a tunnel about midway down (tracks at 128 m) in a superflat 'Tunneler's Dream' world. Running along either side of the rails are single-conductor Redstone circuits with Repeaters set at 10 m intervals. Under each Repeater is a Redstone Lamp which I placed there in order to better see from a distance the signal as it travelled down the Redstone conductors.

The conductor on the left (outbound-pulse POV - see below) connects twelve Detector Rails spaced 100 m apart. The conductor on the right is for another, unrelated purpose. Also, to mark 100 m intervals are ordinary torches set in 1 m deep alcoves immediately below the tunnel's 4-metre-high 'ceiling.'

To the test both circuits' continuity, (it is surprisingly easy to miss a broken Redstone link when there are 2,400 of them to inspect) I bridged the circuits at both ends of the tunnel and then injected a pulse into the right-hand conductor via a Redstone circuit built for the purpose. The signal raced off as expected and disappeared in short order. Twenty-four seconds later it reappeared on the other conductor, raced back to the launch point, crossed the near bridge and then raced off as before. It did this indefinitely provided I did not fly down the tunnel whilst the pulse was still circulating (I should mention here that I am in Single-Player mode and with the visibility set to Far). When I did fly down the tracks I noticed that, at certain places, the tunnel was lit but with no apparent source of light. Sometimes the light would cut off sharply at block boundaries and sometimes not, but in nearly every case these areas of 'source-less' light appeared no closer than 300 m from the tunnel endpoints and nearly always within 10-20 m of a(n ordinary, not Redstone) torch.

Now, here's where things get really weird: Whilst I was flying through one of these weird, lighted areas at the same time the still-circulating pulse raced through, one of two things happen: either the area would become dark, as expected, when the pulse raced off (the light being emitted of course by nearby Repeaters and the Redstone Lamps under them) or the pulse would suddenly assume a duty-cycle of nearly half the natural period of the total circulation time, that is, the pulse duration jumped from its nominal 100 to 200 milliseconds' duration (or however long it takes to move a piston from fully closed to fully open) to nearly twelve seconds - an increase of 12000 percent - a curious coincidence, btw, given that there are 120 Repeaters along each conductor's route.

I made a couple of video captures of this phenomenon, but I'm new here and not quite sure how to get them into your hands. I suppose I could put them up on my Google Drive and provide a link? Please advise.

Sorry this was so long-winded, but I think it best to provide as much detail as possible in the hopes that it is all somehow relevant.

Best,
Tex