Layer separation is removing the middle of glyphs

The `Fast Pixelwise Analysis of Music Document, Classifying` job produces a symbol layer where the glyphs have no middles, like this:

The middle of the glyphs remains in the background layer. We previously thought that this issue had to do with background removal, but it would seem not; I ran this job with layer separation models made in 2020 without background removal. I can also confirm that these same models did not carve out the middle of neumes in 2021 (there is a comparison image [here](https://github.com/DDMAL/Rodan/issues/1201#issuecomment-2614584076)).

The models I used are here: https://github.com/DDMAL/e2e-omr-resources/tree/main/document_analysis/Salzinnes/models. (A reminder that Model_0 is now model 1 and Model_1 is now model 2.)

The image I used is here: https://drive.google.com/file/d/1pa2e_DMGfvwwCpW9424FpHu-d-rZ8nbh/view?usp=sharing

And this is the workflow: [Layer separation.json](https://github.com/user-attachments/files/18579768/Layer.separation.json)