Glitch or bad design during booting on Mojave?

After enabling FireVault with recent T2 firmware patch the loading bar looks weird like its missing pre-cached image:

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I replaced default Mojave.heic with a test image and gray “transparent” area kept test image framed while the rest of the screen remains black after system switched to user scale. Setting Display -> Scaled back to Default returning smooth booting. Is this a design issue or missing cache?