Photoshop 26.1
Windows 19045.3324
Step 1: Open a test image
Step 2: Make a small selection with the polyganal lasso tool.
Step 3: Click Generative Fill, then click Generate
Expected result: The mask for the resulting Generative Fill layer should match the original selection
Actual result: The mask for the resulting Generative Fill layer expands to be larger than the original selection in an octagon shape with feathered edges.