Well, Since 1.5.1 (builds above #771, can't tell exactly which build it started) we started to notice a kind of block lag when breaking blocks/signs while the server is at low TPS (about 13 TPS or less). I'm sorry I can't provide more information on this. I dunno even if it's an Spigot or bukkit issue. The thing is that we sticked with #771 due to this block lag issue and hopping it would be fixed on newer builds. Well, today we've updated to 1.5.2 #884 and the issue is still happening How to test: If you're running at low TPS you may test it by placing a dirt and then breaking it. The block will vanish for a split second, then appear again for a brief moment and then finally drop. Whish I could have tested it better before so I could point out the exact build it started happening. The thing I can say for sure is that the issue doesn't happen on #771, even if you're at a VERY LOW TPS (like 5 or 6).