Morph + Assimilation Aegis is not overwriting copies of the exiled creature.
If you have a face down creature and exile an enemy creature with Assimilation Aegis, then equip the face-down creature with the Aegis, the equipped creature remains 2/2 instead of becoming a copy of the exiled creature.
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Rezzahan#77802 commented
Not a bug. The permanent does become a copy, but is also face down. And face down status (layer 1b) is applied AFTER copy effects (layer 1a).
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Illuminator#91232 commented
Here's a screenshot of the bug.