I have Fox 36 Talas RLC FIT 160, 2011 I believe, upgraded to Kashima. When I lower them to 120 they slowly extend to 160. I can observe the O-ring rising. Takes them about a minute or so. When riding or sitting on the bike, they don’t do it. All travel (all is a bit relative with Fox) works both in 120 and 160mm.
Usually, due to space constraints, I keep the bike standing on it’s rear wheel and then it’s not happening.
Is there a busted seal? I am happy it’s extending itself and and lowering.

Any ideas?

My 2006 Talas reduces travel by itself, a guide on holiday said another rider had the same problem and it was a case of changing / servicing some of the internals.

Seals in talas leg letting air into wrong place by the sound of it, service or Warranty time if applicable.