Opening Joplin files from another computer

I keep my Joplin files on Dropbox. I tried to access those files through Joplin but from my other computer. Though the files were opened, the titles were replaced by some numbers and the end each note contained some code-like text. What is the correct procedure?

(I use the portable version of Joplin.)

(Main computer is on Windows 7 Pro, the other computer is on Linux Ubuntu.)