Hi Alexey,
Thank you for your interest in Syncfusion products.
I was not able to reproduce the issue. Please refer to the test sample in the below link:
http://websamples.syncfusion.com/samples/XlsIO.Web/6.4.0.14/F77383/main.htmCould you please reproduce the problem in the above sample and send us so that it would help us to find the cause of the problem? Also please let us know the Essential Studio version you are currently using.
Regards,
Geetha