Thumbnails using downscaled 256x icons instead of 48x

Hi, I'm running Opus 12 Pro on Windows 10 x64 and I've run into an issue regarding file icon sizes. I'm using a custom set of icons to replace the default icons for common file types, and would like them to display their 48x image. The .ico files for each icon contain images for 16x, 32x, 48x, and 256x images. When looking at the files in Windows Explorer with the appropriate icon/thumbnail size ("Medium icons'), they 48x is properly displayed, but looking at the same file icons in Directory Opus with the thumbnail size set to 48px (or anything greater than 32px, for that matter), the displayed file icon is a downscaled version of the 256x image. I have the advanced setting to use 48x thumbnails enabled, but that doesn't seem to affect the issue. Is there any way I can have Opus use the 48x icons without deleting the 256x images from each .ico?!
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With the advanced option on, what happens if you use Large Icons mode instead of Thumbnails mode?

(You'll need to let Opus restart after changing that option as well. Not just close the window but via File > Exit Directory Opus.)

Even after restarting the program and/or PC, the issue persists, and using the Large Icons file display mode displays the 32x icons rather than the 48x icons.