After deleting a block from the list of blocks the focus apparently remains on that (now non-existent) block, you can delete it again and again. Moving the focus to the next block in line would be the expected behaviour, just like in every file manager, text editor etc.
In the layer list the focus jumps to layer 0. That's better, but I personally would prefer it to jump to the next in line.
Speaking of those lists it would be really cool to select multiple entries for joint deleting, editing properties, hide or display.