Consider the following code:

int numberOfImages = [1 or 2];
QString fileName = "someFile.jpg";
QString windowTitle = QString(i18ncp("@title:window", "Copy %2", "Copy %1 images", numberOfImages, fileName))

The singular case correctly displays "Copy someFile.jpg"

However, the plural case, displays "Copy 2 images(I18N_EXCESS_ARGUMENTS_SUPPLIED)"

In fact, there aren't excess arguments, it's just that both variables aren't used in each string. But besides the error message, the output is otherwise perfectly valid.