Custom Steel with Shimano 105 triple brifters - a 3-4 of years old.
Took my old bike out for a ride after leaving it forelorn in the basement (using my new Madone mainly since October) and went for a ride. Going along in the middle ring fine. Changed to large ring and then it would not shift back down. It appeared that the downshift mechanism was seized. No action - that is the lever would not move. Of course, it happened on a rising grade. Managed to get it to finally shift after futzing with it for about 3 minutes off the bike. Same thing happened a bit later. Was careful to finish my hilly loop without moving to the large ring. The middle and small rings worked fine repeatedly, both up and down.
Was just down in the basement with it up on a stand. It appears to be shifting but may be catching a bit if I don't immediately release the "inner or smaller" brifter lever. I do recall getting a new chain on this not long before moving to the new bike. Oh, it is a 9-speed, I believe, but customized to only 8 in the rear (xt mt stuff moved from a rusted custom road frame that had bar-end shimano. There were no problems prior to this for those 3 or 4 years. Possibly the new chain had/has something to do with this?
I am not much of a bike mechanic, frankly.