Failure when converting editor format to storage format in 5.1.3

Version: Atlassian Confluence 5.1.3
Issue: Receiving "Failure when converting editor format to storage format" error when trying to save a page.

Description: When copying and pasting text from Sprint! (JIRA) into Confluence Editor, that has mark-up icons like to insert a question mark image, which is then deleted, when I save the page I get this error.

Steps to reproduce:

1. Copy already saved/posted text with mark-up icons from Sprint! (JIRA), such as the following without quotes: " test test test"
   • In JIRA, this text will show up as a "?" icon image followed by the text:
   • 
2. Paste this text into the Confluence editor.
3. Delete only the icon character, and not the entire string of text.
4. Attempt to save the page and get the following error:
   • 

If I click the < > button to get into the XML editor I get the following error:
" Error loading source
RuntimeException occurred while transforming editor format to storage format (java.lang.NullPointerException) (500)"