Hi Dmitriy,
Thanks for your interest in Syncfusion Products.
The double pasting issue in MDI child has been reported before and fix has been provided in a patch in v8.1.0.30 in the following forum thread. Please refer to it.
http://www.syncfusion.com/support/forums/grid-windows/93467This fix is publicly available in our latest version 8.2.0.18. Please refer to the following forum thread for details regarding the fixes available in this version.
http://www.syncfusion.com/support/forums/general/93921Regards,
Rajadurai