This is not a bug. It is how the Inventory Quantity Movement report was designed. It’s a well-known characteristic of the program and has been discussed in the forum previously. It is a true movement report, as titled, not an inventory on hand summary.
I agree it would be a good idea to have consistency between the two reports and the ability to create a report showing all inventory quantities. There has been such a suggestion in the ideas category since May 2018.
I am taking this out of the bugs category, because the program is functioning as designed.