A filled shape appears unfilled if I resize the image down to 62x62 down to 45x45. If it is smaller (44x44) or larger (63x63) it appears filled. I have not checked for other "gaps" like this.
1. Your Mac’s OS X version (Apple Menu > About This Mac)
2. Your Mac’s specifications (Applications > Utilities > System Information > Hardware Overview) and especially its Graphics/Displays information
MBP 13" Mid-2014
2.6 GHz Intel Core i5
Intel Iris 1536 MB
3. Pixelmator version (Pixelmator > About Pixelmator)
Version 3.6 Cordillera (61103)
4. A step-by-step explanation of how to reproduce the issue
I'm not sure how to recreate it. When I tried to duplicate it more simply from the evolved file I'd started with, it works fine. I may need to send you my file. The steps I *thought* would duplicate it are:
Start a new file TEMP at 256x256 resolution.
Created a shape from a single black-filled text glyph. I used ⬍.
File > Duplicate, rename to TEMP@2x.
Image > Image Size to 60x60. Shape appears unfilled. Try other sizes and notice which show it correctly filled or not.