When Dupes dig out some blocks, the bar will be full but the dupes will continue to try and dig it forever, if you cancel the dig order then you cannot do anything in that space anymore, and even though graphically there is nothing there, Dupes will move around it like the block still exists.
Steps to Reproduce
Just regular digging
Status: Known Issue
We are aware of this issue and have it logged internally but either we do not have a fix ready yet or we are not planning on addressing the issue in the immediate future.