You can add an effect four places:
1. An event – only affects that event
2. A track – affects all events on that track
3. Media Pool – Affects all events in the project from that piece of media
4. Preview screen – Affects the entire project
Sounds like you have placed it on #4 and, maybe, should have used one of the other options so that the JPG event does not get affected.
Edward Troxel