at large distances from the centre of the world, when a detector rail is has a minecart placed on it, and is moved by a piston in unison with the minecart, the detector rail appears to lose track of the minecart and becomes unpowered despite having a minecart on it. Providing a block update does not fix the issue.

While I don't know the lower bound on how close to the world centre this can occur, I know that it happens anywhere beyond 15 million blocks away

Edit: with some testing, I've found that this only occurs at distances greater than or equal to 16777216 blocks from 0 0 0 on either the X or Z axis. As long as the position is less than that on both axis, there is no issue. This also happens to be exactly equal to 2^8. This (at least to me) suggests this is a data type limitation, meaning that the position is being handled with the byte data type in java, which consists of 8 bits and can store any value equivalent to 0–>16777215 in base 10. this could be resolved by using the short data type, as it is 16 bit and can thus handle any co-ordinate values within the minecraft world.