From time to time I noticed strange filenames on the Synology Diskstation. Names like BGELMF~0. They always had a tilde. Those strange names are called mangled names. Samba has a feature to provide them to bad clients. Unfortunately this can also lead to “renaming” those files.
It is better to prevent this behavior altogether. To do this you need to connect over SSH to your diskstation and then you need to login as root.
Issue the following commands:
cd /usr/syno/etc vi smb.conf
Now insert the following line in the section global:
global mangled names = no
Notice: this option could be reset after an update of the diskstation. If the bad filenames appear again, you should verify that the settings is still active.