This has been happening for a while now, atleast the last 2 versions of the Android App.
Problem Description: With Subsonic App running in background, focused, or closed, If you mount the phone as a Disk Drive to a computer then when finished and disconnect the SD card will mount on the phone. After this happens Subsonic will start playing the file that was last opened.
Troubleshooting Steps: Installing new versions of App and restarting phone.
Playback Application and version: Android App Version 2.7
Phone and OS: HTC EVO 4G Android 2.2 Stock ROM
Server Version: 4.2 (build 1944)
Any ideas?