Repeaters become a level pulse if two or more are connected in series(Also, without any redstone dust or a block between each repeater) and set to the same amount of ticks as a clock connected to them has. I think that the first repeater "stretches" the pulse, and then the second repeater glitches and thinks the stretched pulse is shorter than the original pulse, which would mean that the stretched pulse is shorter than the delay of the second repeater. This might cause the second repeater to stretch it again, but it stretches it into the next "glitch pulse" it receives from the first repeater, becoming a flat, unchanging state. (Doesn't occur prior to 1.8)
I tried doing the same thing, but putting a piece of redstone dust between both repeaters, and it worked like it should have.