Attachments with plus signs in name not downloadable

I've uploaded an attachment named "Stichwortliste 365+1.xls" into Confluence and embedded a link to it in a page.

The link is converted to

<a class="filename" href="/download/attachments/5275808/Stichwortliste+365%2B1.xls" title="Stichwortliste 365+1.xls">

But I can't

• download it from the link
• access it in the attachments' section of the page
  (There only works "View")