dropbox destroys files: what did I do wrong?

Friends--

A saga in which our protagonist (me) loses thousands of files and has no clue what he did wrong, and hopes someone in this realm can point out to him the quicksand so he does not step in it again....

Have used dropbox for 2 years or more in a production environment, with ne'er a lost file.

Recently I got the bright idea to use it to back up much of my data files. Desktop (D) box is connected via cifs to Ever at the Ready server (E) for data files. D is connected to Web and to dropbox. Not wanting to duplicate all E's files on D, I did ln -s /path/to/server's/data/files in my ~Dropbox directory.

A week or so later someone sharing files via a private dropbox folder said they did not see the newest files in our shared dropbox folder. Then another person did not see some other new files in a different shared dropbox folder. I checked it out: the files were in my local dropbox folder, but not in the ones on dropbox.com.

Suspecting the dragon in the woods to be the huge numbers of files from my server (clogging the pipeline to Dropbox.com), I rm the directory from my ~Dropbox folder. Now the missing files appeared on Dropbox.com and in my correspondents' respective folders.

All was well, I thought.

Alas, it was not to be: whole bunches of my data files had disappeared from my server! Not every file in every directory; not every file dated before or after a certain date. Sometimes whole directories, sometimes just a few files here and there. Not any particular file type.

Luckily our protagonist had lots of backups, and was able to restore everything (he thinks). Not so luckily, he used a whole weekend of very pleasant outdoor weather inside carefully restoring files!

Where did our hero go astray? Where be the dragons and quicksands of this realm which might be avoided?