To reproduce you may need to check out the web-platform-tests locally, and run the server, as described in the README.md file . When run locally http://web-platform.test:8000/2dcontext/fill-and-stroke-styles/2d.pattern.image.broken.html seems to flip between passing and failing. When run on w3c-test.org this doesn't happen, presumably because of the increased latency. This suggests some kind of race condition in the loading code. (that also suggests that this might not be a canvas bug. But a good fix might be to make this test always pass, which might be possible without fixing the underlying race since, presumably, the image is always known to be broken when createPattern is called).  https://github.com/w3c/web-platform-tests
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