Hey there,
This is caused by a recent change introduced in the Wine Cellar patch.
Private server owners can change this setting by adding or modifying the following line in ServerSettings.ini:
VocalVisibilityDurationInMinutes=x
Where X is the duration in minutes a player will be listed in the player list after participating in chat. If you set that value below 1 minute, this feature will be disabled (this is the current setting in official servers at this moment subject to change in the future). Any value set to 1 or above will show the results reported.