Workaround for the sound from internal earphone bug on 681 ROM
Before Sony release their new ROM to fix the sound from internal earphone bug on 681, there is a workaround to get rid of it.
Make a call to any number, switch to hands-free mode i.e. sound will come from the external loud speaker instead of from the internal earphone. Do not switch back, just hang up the call. Now the sound will back to normal.
BTW on how to check whether your phone are currently in the buggy state: go to system settings, sound, check ringtone or notification sound and click to preview the tone. The sound may come from the earphone instead of the speaker. This usually happens after a call that end with earphone in use. This seems does not affect a phone with bluetooth earphone.