Hello! This is expected behavior. Alpha and Color may be different inputs, but both values are used in the final color calculation. So, Alpha can affect the color based on the shader's blending mode, particularly if it is outside the expected 0-1 range.
To ensure your shader works in all contexts, we'd recommend clamping the value to the 0-1 range. As noted in your report, using the Saturate node is one way to achieve this.