The decimal values are exported using the symbol defined in the thread culture. However, they should always use the period as a decimal symbol. The wrong value can lead to wrong resizing of the image inside the exported document.
Workaround: Change the current culture settings of the thread before exporting:
string cultureName = Thread.CurrentThread.CurrentCulture.Name;
CultureInfo cultureInfo= new CultureInfo(cultureName);
if (cultureInfo.NumberFormat.NumberDecimalSeparator != ".")
{
cultureInfo.NumberFormat.NumberDecimalSeparator = ".";
Thread.CurrentThread.CurrentCulture = cultureInfo;
}