404 errors with Chart macro when overriding webwork.multipart.saveDir

As per this documentation in regards to home directories.

An alternative directory may be specified for temporary data by setting the webwork.multipart.saveDir property in confluence.cfg.xml.

However, by doing so, the 'Chart' macro crashes: images are generated inside the folder, but the HTML is still using the %HOME%/temp and we have an error 404 (file not found) instead of the image.

Steps To Replicate

1. Create a page
2. Insert a chart using chart macro
3. Edit confluence.cfg.xml
4. Override webwork.multipart.saveDir to an alternative path
5. Restart Confluence
6. Open the page again