phone line conductor reversing

I have standard phone line via pole, all very rural (59db attenuation according to my brand new replacement modem). A few years back we had ADSL troubles with ADSL disconnecting when the phone was used and noise on the voice line. This was after an engineer visit from open reach. By some miracle I thought to switch the two line conductors around which cured it. Having recently had the engineers round again the fault reappeared but not immediately. Cured it again by switching the conductors back. Any idea why this happens, I thought the conductor 'sense' didn't matter. Is there some underlying issue?

The bulk of the ADSL signal is down the B leg of the pair, hence sometimes folk on here reporting no dial tone, but still having broadband, albeit at a somewhat reduced rate.

Not sure if this has any bearing on what you are experiencing, because a reversal of the lines polarity shouldn't make any noticeable difference unless it's after the master socket.

Thanks. It is after the master socket. I don't know the reason for this effect nor why it suddenly caused noise on the voice line after a couple of weeks. Did occur when I changed the ADSL router so maybe it's to do with the DSL input circuitry.

All the A/B 2/5 after those in the NTE should be the same, this can cause issues with ringing, faint transmission on cordless phones, and other weird do-do.

Ah there's a thought. It is a chordless phone.