On what computer operating system is your Premiere Elements 13 running? Have you updated from 13 to 13.1 yet? If not, please do so.
Assuming that you are not misinterpreting any of the workflow for keyframing volume property at Timeline level or in Adjust Tab/Adjustments Palette/Volume expanded, please delete the Adobe Premiere Elements Prefs file (setting file). For Premiere Elements 13/13.1 on Windows 7, 8, or 8.1 64 bit
Local Disk C
and in the 13.0 Folder is the Adobe Premiere Elements Prefs file that you delete. If that does not work, then delete the whole 13.0 Folder in which the Adobe Premiere Elements Prefs file exists. Be sure to be working with Folder Option Show Hidden Files, Folders, and Drives enabled so that you can see the complete path cited.
Please review and consider, and then we can decide what next based on the details in your reply.
I upgraded to 13.1, removed the file, restarted the program and - lo and behold - that seemed to do the trick.
Thank you for the update with the great news that your Premiere Elements 13/13.1 is working for you. Great job.
We are glad for the opportunity to be of assistance.
Best wishes as you move forward with your Premiere Elements workflows.