Every once and a while you may try to insert a block into your drawing with the Library Manager and the geometry seems to change from the source file after the insertion is complete.  The answer to the problem lies within the existing definition of your open drawing.

The reason the new block does not look correct is typically because the existing definition, with the same name in your file, does not match the new set of geometry.  Simply enter RENAME at the command line and in the rename dialogue box, highlight the listing for Blocks and then find the name that matches your problem block.  Rename the block to something that describes the geometry and pick the OK button.  You can now insert the block with the Library Manager and the geometry will be the same as the inserted file.

If you do want to replace all of your existing blocks that are named the same, use the AutoCAD insert command and make sure you pick the yes button when prompted to update the existing blocks in the drawing.