Sunrise works with 3 type of orders:
Customer orders (From the channel to the customer)
Channel orders (From the merchant or central warehouse to the channel)
Inter-warehouse orders(Moving stock between different warehouses)
Every time a webshop or warehouse order is created, in addition of the Customer order, Sunrise internally creates a secondary linked channel order from the Merchant (channel 0) to the channel.
They are not double because their order type, but they are very useful as an internal reference when you work with multiple channels, specially when the stock is consumed from a central warehouse and shipped in the name of a channel (webshop and warehouse orders).
So for example if you start a franchise model , you can deliver goods in the name of the independent shops (channels) from a central location, but internally you could invoice these orders to the channel even with a different cost price.
This is not mandatory and you can work without using this features but its built in.
This is why you see the Webshop and warehouse orders orders twice when you select order type All.
The best is to select only Customer orders or Inter-warehouse orders.
Channel orders are also relevant when you ship goods from a central warehouse to a shop warehouse. In this case the order is not double but you could also use them to invoice the specific channel when stock is replenished from a central warehouse.
Hope this clarifies your question.