Hi Yves,
Thank you for your interest in syncfusion products,
I am afraid that I unable to reproduce the issue. Also I have created a simple sample to test this issue and it is available in the following link.
http://www.syncfusion.com/downloads/Support/DirectTrac/90098/CS781816438.zipPlease have a look at the sample and if still the issue exists, could you please try reproducing it in the above sample so that we could sort out the cause of the issue and provide you a solution?
Regards,
Ragamathullah B.