I believe I've found a easy workaround to problems while editing, copying and saving equations.
But first, how I got here. Everything had been working fine with Word 2013 for me until few days ago when I was working with equations. I was specifically editing, copying & pasting equations within the same DOCX document. Word started freezing up and would not save during exiting the Word application. Word would just freeze and hang forever. My CPU and fan would go on full blast loud.
I had tried every possible troubleshooting procedure in these forums and knowledgebase articles including:
1) installing Office Compatibility Pack (even though I don't need Compatibility packs since I don't use older Office programs)
2) attempting repair of the Word document
3) removing all "add-ins" and trying Safe modes (I don't have ABBY fine reader)
4) repair of MS Office Pro Plus 2013
5) "clean" install of Windows 8.1 Professional on a relatively new 6GB RAM touchscreen PC with 400GB free hard-drive space
6) "clean" install of MS Office Pro Plus 2013 using MSI Installer / DVD
7) Applying all Windows Updates including Office 2013 Service Pack
8) Went to another computer that runs Windows 7 Enterprise with Word 2010 and this too showed the same problem.
Despite trying the above, Word 2013 continued to freeze and hang after working with equation editor and trying to save & exit.
Simple Workaround: CLEAR CLIPBOARD memory from Word after working with equations. Easiest way to do this is to either (1) do a "Clear All" from the Clipboard Icon in MS Word on the Ribbon, or, (2) just copy some text in your document and paste right over it before saving document or exiting application. This clears the Clipboard memory. Each time I did this, I had no problem!
It seems that Word is unable to handle something in RAM when working with equations and so emptying the Clipboard manually resolves this.