<edit, I realized the underscores I typed got interpreted as formatting in the post so it made no sense; I retyped it>
I was changing all instances of one tag to a different one so I filtered a Pane on the tag to change and replaced each one manually. I was left with a single item matching the filter that should not have been included. It is a [[Linked item and the original item had already been updated to the new tag. That original removed itself from the Pane, and the text of the [[Link updated correctly – but the item containing the [[Link remained in the filtered Pane, even though it shouldn’t have. The only difference between new and old tag is that the new tag has an underscore in it. I believe the _ in the tag is being ignored by the filter.
I tested this with another tag by inserting an underscore on an item that was linked-to. The filtered Pane still showed that item.
I also tried inserting the underscore elsewhere in the tag, such as arbitrarily in the middle of the text. The behavior is the same as when the underscore immediately follows the #.
