Bike is an '09 Meta 5.5 with stock kit.
Chain is spotless with no stiff links. Indexing is spot and shifts crisply.
The problem is occurs when pedalling backwards for more than 2 pedals. The chain jumps to the next highest cog. The dérailleur stays where it is (no change in cable tension) and chain slips off the top jockey wheel.
Pedal forwards and it engages in the proper gear.
Its not a problem unless I pedal backwards (doh) which is rare.
I've never experienced it on other bikes I've owned.