No I sussed it yesterday but I thought I'd hit the international updating-your-own-blog-posts 'nerd threshold' and decided not to bother. But since you ask... it's the fact that the pin from the SIL module that you connect via an LED and a resistor to VCC to indicate transmitter activity, doubles as the TRANSMITTER LEARN command if you connect it to GND instead. So by e.g. soldering the SIL side of the LED wire without unplugging the power (path to earth, albeit tortuous, via soldering iron!), and a number of other fiddles, I've been accidentally telling the receiver to learn a transmitter that never transmits -- because I didn't realise I was pressing it.
Make sense? No I didn't think so.
You are right about RFI being a bastard around here though. I blame the station, or the taxis, or the CI tower, or all three. My RF shed alarm didn't work because of it. Also the doorbell sometimes rings when it shouldn't (including when the neighbour's bell is rung, but that's another story).