Strange behavior indeed. Make sure to check the oil level on a flat surface when the car is level.
Other things to consider: How old is the oil? Are there other issues with the engine? Oil viscosity?
My recommendation: Add half a quart to see if the "low oil" message returns. If it does, add another half. Drive it until you need an oil change. During the oil change, note how much oil is drained. Fill with the proper amount of oil and see if the "low oil" message returns.
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