When we print from the voucher which is opened in Display mode, the report VCH Display is getting printed. Hence, need to add the customised print report in the form of VCH Display.
Example
[#Form: VCH Display]
Add : Switch : TestSalesPrint : TestCustomSales : $$IsSales:##SvVoucherType
[!Form: TestCustomSales]
Delete : Print : Voucher Print
Add : Print : TestCustomizedVCHPrint