Attachments with '+' symbol in the file name give "page not found" error

A customer attached a .PDF file to a page in their instance but when they then try to access the file they receive a "Page not found" error message. Removing the + symbol resolves the issue, as can be seen from the example below:

• NI-Hildesheim_HRB_3196+Aktueller_Abdruck-20120305093945.pdf
• renamed NI-Hildesheim_HRB_3196 Aktueller_Abdruck-20120305093945.pdf

This issue has been confirmed with a .PDF file but most likely will affect other attachment types also.