As MC-186701 is no longer open, I'll add some of the information here as well.
The issues start with the detector rails when either the X or Z co-ordinates are greater than or equal to 16777216, or 2^8. Seems like an awfully big coincidence that it occurs after exceeding the limitations of an 8 bit number, but obviously it could be for a variety of reasons none of which I am informed enough to speculate on.
This bug, for me at least, has been a pain to deal with. I ran into it while trying to make a vital redstone machine on an anarchy server (the kind of server where you want to be extremely far from spawn) and as a result, we have to abandon our current location entirely and move closer to the world centre where this won't occur.
I'm sure that this has been a problem for other people, albeit for perhaps entirely different reasons.
Ill talk to the owner and try to get a copy of the log