Somehow all of my quote history disappeared, and I believe I can recreate the problem. It appears that invoking the command line processing to add quotes to the data file, is actually wiping out all quote values.

Start gnucash, Select Tools / Price Editor
Select Get Quotes. 
Quotes are downloaded as expected and can be displayed.
Close gnucash and reopen gnucash, quote history is still present. 

I then run /usr/bin/gnucash --add-price-quotes=full_path_to_gnucash_file

While gnucash returns a successful exit code, upon starting gnucash again, there will be no quotes. I also tried it without the equal sign between the command line directive and the gnucash filename, with no difference in behavior. 

Can anyone else verify this and/or is additional information necessary?

Thanks