Try it on a 20hz clock. Its still apparent in 1.8, as of recent testing.
also confirmed.
Also, see this tweet from Searge:
We are not going to do any performance optimizations until 1.8 is feature complete and we start the buffixing and polishing stage.
Seems to have broken, but the other way. On 14w25b I cannot get the name of an item to display at all. I'd only assume its the same for the rest of the technical items too.
Command: summon Item ~ ~2 ~ {Age:-32768,PickupDelay:32767,CustomName:"Defenders Captain",CustomNameVisible:1,Item:{id:minecraft:diamond,Count:1},Riding:{id:WitherSkull,Invulnerable:1,CustomName:DefCap,CustomNameVisible:0,direction:[]}}
Confirmed for 14w07a
Confirmed in 1.7.4. Still annoyed this hasn't been fixed >.<
During testing, I was using a 20hz clock (the setblock / fill ones) with the command:
/effect @p 4 60 3
The issue may be that the client is refreshing the mining fatigue, so that you cannot mine anything as it keeps resetting your break.