It's been a while since I experienced this but from what I remember it was always with the Unbreaking enchantment on. To me that suggests a calculation of amount of durability left before calculation of unbreaking effect.
I.e. Pickaxe has 1 durability left.
I use that 1 durability and pick breaks
Unbreaking effect is then calculated, and says nope it didn't break.
Not saying thats a conclusive answer or anything lol
If it was just a server lag problem I would have thought it would not exist in Single Player as well?
Yeh I won't complain about getting full use out of it. If I try really hard I almost convince myself that I'm getting more than I should lol
The only reason I'm saying anything is just the annoyance of having to do a pile of clicking when the game should remember what's left durability wise. =)
It's on single player I've noticed it but I don't play a great deal on smp so it may occur but I haven't seen it. I'm a fairly new player so I don't have much idea of what's old and new. It's more an annoyance by the old reporting system.
This behaviour comes from the new stair wrapping. The lower set of stairs is convinced it should be wrapping hence the small square on top. The stair isn't actually the wrong way it just appears to be due to the half slab next to it.
Also F3+H(PC) works way more effectively at preventing you from going through a pick/tool you don't want to lose rather than hoping on a random bug to occur.