I made a simple outline shape of clothing and applied a Fill and a Stroke of 6 pixels wide.
Note the line very tight in the red highlighted portions above.
When I export this as a SVG format, it appears quite different rendered on a browser such as Chrome:
Since there is significant difference between the two I'm reporting it as a bug. Both Firefox, Chrome, and Safari render the image closer to the bottom image.
Thanks for all the great work with Pixelmator.