Strange DCC loco behaviour when programming other locos

[81F]

Just as an introduction the Bachmann locos I refer to are British outline from the Bachmann Branchlines Range.

Among my collection I have six locos fitted with the Bachmann EZ command 21 pin Decoder 36-554. All work very well and were fitted and programmed without a problem using my Hornby Elite DCC controller on a fully isolated programming rail.

However, the last loco (an LMS 3F) has been behaving oddly when I have tried to programme other locos. Despite being on the main layout which is isolated from the programming track it runs at high speed when I try to programme other locos. The really odd thing is the all my other locos on the same track remain stationary (including the other 36-554 fitted ones).

Has anyone else had this happen to them? 

[bapguy]

Have you changed any thing on your layout lately? IE wiring or scenery? Does your programming track have both rails isolated? It sounds like on the problem loco it has DC enabled in the decoder. Some how when you program a loco, the DCC signal is crossing the gaps to the main track and if the loco has DC enabled, it might read the signal as full DC and take off. Joe 

[81F]

Thanks joe, just checked the programming rail and it is still isolated (with two plastic rail joiners). Oddly all my DCC locos are programmed DCC & DC but this is the only one that does it.

I will probably re set the Decoder (CV8 = and reprogram it and see if that makes a difference.