I ran into this bug also. In addition, if I delete the sole object in a block and save the file, when I import it into my CNC cutter, the object still exists until and unless I delete the block it used to belong to.
If I delete the object in a block, should it not delete the block too?
EDIT: There seems to be a bunch of glitches surrounding blocks. If I cut objects in blocks and paste them back, it pastes them as new block names (adding a -0 at the end). If I undo the paste and also undo the cut, the duplicated block names remain. If I cut and paste block objects they don't import into my cutter software any more. That may be a bug in the cutter software, but it at least indicates that something besides just the position is changing in the save file.