Plugin generates relative links but it doesn't put the / in front since by
default CMSMS has a base-tag.

This base-tag can be disabled by using {metadata showbase="false"} in the
template
If we do this, the links relative links generated by the plugin aren't correct
anymore, since they miss the root or "/"

so if your page is example.com/library/productsheets -> the links point to
example.com/library/uploads/link/to/sheet.pdf in stead of 
example.com/uploads/link/to/sheet.pdf