Gamma boost with filter or lower 3rd

Today I noticed a strange issue that I hadn't seen before. When I put a lower 3rd (uncompressed avi with alpha channel) over video, the video level of the underlying footage gets a gamma boost. This boost only happens in the area of the timeline where the lower 3rd is located.
In attempting to resolve the issue, I put a levels filter on the footage. By placing the filter on there, and not making any changes I noticed there was no jump in gamma when the lower 3rd came on screen. I soon realized that the entire clip now had a gamma boost on it, instead of just the section of the clip with the lower 3rd. To correct the issue, I brought the gamma level down from 100 to 89. This is my current work around for the issue, but I'm wondering if anyone knows what is causing this and how I can avoid having to use the work around. I'm using Premiere Pro 2.0, editing on an NTSC DV timeline with NTSC 29.97 DV footage.


Los Angeles, CA
www.chadsimcox.com