Preview New from clipboard drawings copied from Microsoft Powerpoint have inaccuracies

I'm using Microsoft Powerpoint and Preview to make drawings for my thesis report using the following method:

• Create lines, text, + shapes drawing in powerpoint
• Copy the drawing elements to clipboard
• Open Preview and select File -> New from clipboard (this creates a pdf of the drawing)
• Save pdf file for use in Latex report

This has worked in the past but now I notice the drawings in preview are poor quality, with many visible aberrations, compared to the original drawings in Powerpoint.

Here are two screenshots to illustrate the problem.

1. Screenshot of original drawing in open Powerpoint file

2. Screenshot of pdf file in Preview with annotations to highlight selected aberrations

Note that in the drawing after importing into Preview, some off the circles are oval-shaped. One of the arrows does not align with the circle.

Anyone know what is causing this? How to fix it, or an alternative work-flow that would achieve what I am doing (I want vector graphics drawings not raster graphics for the latex document).