Hi "terencino",
I see the same as you with the "Custom Dictionary.txt" file in the "Downloads" folder.
For me it only works once. When I do a fresh install, and start up Evernote - this file is being filled up when I add new words to the dictionar.
However - if I now reboot the PC, no words are being added to this file no more. It seems to me that it only works once :-(
Hoping for a speedy recovery of the spell checker :-)