apper: Apper can be run only from the KDE menu. When I create a link or a copy (of the desktop file) in my "util" folder and run apper from there, it will run but on closing I get "KDEInit - cannot run /usr/bin/apper" and a bang. Only when running from the KDE menu, apper will close quietly.
sound: Sound resets itself to 100% repeatedly. For example, the bang from apper is really a bang. Lowering the sound volume in the settings is futile, next time I get another bang.
desktop files: Plenty of nuisances, sorry. Sometimes, copying a desktop file results in making a link instead of a copy (libre office), sometimes the desktop files are plain text (yes, they are, but they should be run). Sometimes, renaming the desktop file (for example, removing the .desktop extent) loses icon and functionality.
On the other hand, firefox can play videos. Splendid! Copying big data from a DVD seems to copy what should be copied. Splendid! I like Stretch... well, except apper and sound control and...

HW: Dell Inspiron 17R. 8 GB memory, 1 TB disc. Debian installation: netinst CD, no meddling with the installation.