The CCC layout algorithm is usually able to conciliate the specified axis offsets, which impose margins, with tick labels overflowing from an axis panel. When the label overflow amount is already covered by the offset margin, then the layout is valid. Otherwise, the algorithm asks the parent panel for additional padding to encompass the overflow.
Due to not reconsidering already requested additional paddings, to processing labels' overflow before axis offsets, the algorithm sometimes asks for additional paddings even though the offset margin would cover it...
The attached image shows the result of this bug. The observed right margin was added to account for half of the right-most X axis label, that overflows from the axis panel. However, the specified axis offset of 10% would be able to cover the overflow.
The image results from the following chart definition:
The bigger the label overflow, the bigger the added, wasted margin.