That's not a bug, it's a consequence of having transparent data and using interpolation. When interpolating the new values for pixels, the values of neighboring pixels contribute -- including the transparency values. And, depending on the resampling, you can end up with partial pixel coverage that needs antialiased edges.
Unfortunately, there is no good solution to the issue. It sounds simple when you think about a rectangle, but not so much when you think about a layer that has a flower arrangement with transparency.
If you know you don't want antialiased edges, you can change the resampling method to Nearest Neighbor.