[Container] Layout mode grid resizes incorrectly if max width is applied to the container

[juw177]

1. Using css styles, set a max-width for the contents of the Container component, eg, 1200px. Set margin left and right to be auto so that the content is centered. This is a common style used for page content containers.
2. Open page editor and drop a container with responsive grid layout
3. Drop a component into the container
4. Go to layout mode and resize the component.

Results: the resizer does not snap to the grid and will resize to something different to where I drag the resize marker to. This only happens if the max width limit is in force. If I reduce the browser window width to be smaller than container max width, the problem goes away.