Hi Youngjin,
Thanks for using Syncfusion products.
The issue "The diagram builder and symbol designer cannot be restored when I click window taskbar after minimize" reported by you have been Suspected to be a defect. We will fix this issue within 15 business days. For this, Please create a DT incident for your query so that we can update the patch for this feature.
You can create the DT incident from the following link.
<
http://www.syncfusion.com/account/dashboard>In the interests of maintaining confidentiality, we have a policy of not sharing patches or otherwise proprietary customer specific information in the public Forum.
Please let me know your concerns.
Regards,
Amsath Ali.M