I took out and cleaned/oiled the inner wire as i though that could well be the issue as it is problem indexing both ways and any form of snagging would cause that, but no. I have also just "popped" the old 11/32 back on and it indexed fine so I could just be going beyond the design capability of the Altus - but i am going to check the alignment before doing anything else as that sounds good practice whatever.Shame about that! I would tend to go for a long reach derailleur so not to use extension, but only if the alignment tool does not work, and possibly a new inner wire.
Halfords have the Deore at £28.99