Bit of a niche issue, in that it requires the poster has the ability to post html, but reporting it anyway...not expecting a fix on it.
Steps to reproduce:
Allow the ability for your account to post HTML (edit group, enable the 'Can post HTML?' setting)
Create a new topic
Upload an audio file, click it to insert into the editor, and submit
Hover mouse over audio player - no tooltip, as expected.
Reply to the topic
Upload an audio file
Enter some text in the editor, and press return/enter
Click the audio file to insert it into the editor
Submit the reply
Hover mouse over audio player - no tooltip, as expected.
Reply to the topic
Upload an audio file
Enter some text in the editor - do not press return/enter
Click the audio file to insert it into the editor
Submit the reply
Hover mouse over audio player - there's a tooltip, and you may also find that the number of downloads is incorrect (the above screenshot is for a file that has just been submitted)