Just block lag. If you go through your video settings and set anything you have on "fancy" to "fast" that might mitigate it. From what I've experienced it usually happens when there's a mix of placing or breaking tons of blocks like you're doing plus a whole ton of people being online. If you have Optifine, that might help a little too if you turn off some of the extra features.

 

^^^
What Steve said. Might I also suggest the Help Section of the forums for future reference?
Also, I would recommend Optifine as well. Definitely helps with the FPS and block lag.

 

Moved to help/support.

 

Or you can get a new laptop. Or maybe a ghost is removing ur blocks

 

Just normal block lag. I would suggest using a lower pixel texture pack, such as faithful or the normal texture. That'll help a little bit, but not a whole lot. I've got a decent computer, and it still happens to me. You'll still get the block lag no matter what. Nothing to truly worry about.

 

That's totally staff material...

 

I get a ton of block lag now, more than I used to get and it's odd.
Whenever I'm replanting, or laying down ores to fortune, or anything that involves placing anything anywhere. I get block lag.
And I think it's something to do with an anticheat, and if it is, then the plugin is too sensitive :p I can barely place 2 blocks a second.

 

We do not lock help and support thrads, as the problem may re-arise.