If you use master pages and have a text style for titles set on both pages.
If you apply a master page on one side(left) with the title that is used in TOC and another master page for just text(right).
The other side that is hidden because of text master page is set to right side, the title there is added(from right side of master page with title) to the TOC, but it should not have, because the right side has other master page set.
It should ignore all parts if the other side has some other master page applied to it.
Hope I made it enough clear.
Can provide the file if necessary for dev.
THX