Usually when a tab is already open and user receives a new message for that tab, it won't change into red tab name and won't flash in the taskbar. But when a user is picking an emoticon to insert and emoticon picker is open during the message arrival, then tab is showing with a red (unread) title and it flashes in the taskbar. Clicking on a tab doesn't fix the issue. One has to switch tabs or minimize and bring that a chat window again to get rid of this effect. This will happen only in rare occassions, so not a major issue. Emoticon picker is used a JPane and it probably sets a focus on it, so active tab is considered a background in this situation. But at least it should get the focus back and remove unread message effect when a user clicks in the tab area.
Another side effect reported in https://discourse.igniterealtime.org/t/spark-2-9-3-fake-blinking-if-smiles-are-open/89055 is that if you open the picker and then click somewhere outside the chat window, the window will start flashing in the taskbar as if you received something.