Why does wide angle lens adapter + large aperture make images blurry?

I have a kit 18-55mm lens on my Canon. I also have a .45 wide-angle lens that I use on the kit lens. The results are fairly sharp.

When I try to use the .45 wide-angle lens on the 50mm @ f/1.4, it produces blurry images. Changing the aperture f/5.6+ on the 50mm, the images become sharper.

The 50mm produces good images, so it's not the 50mm lens. The 18-55mm also produces good images by itself and with the .45, so it's neither the kit lens, nor the .45 wide-angle lens.

Keep in mind that I manually focused, had a tripod, good light, and was shooting still photography.

So, why is this happening? Why can't I use a wide-angle adapter on my 50mm at a large aperture? And why does it make the photo blurry?