I've downloaded 3.7 version and i made some tests.
Here steps to reproduce :
Create a Sales Order (customer : Joe Block, one line : Mary_Mary Consultant (qty1))
Now, open Generate Shipment form and choose it.
Validate. A shipment is generated. Great.
Now, void the shipment.
And try to select again the order in the Generate Shipment form…
That's just impossible !
It seems that when you complete a shipment, the flag isDelivered is set to Yes in the order.
But it nevert turns to No. And the order is always delivered. You have to ship manually.
Is this a bug ? or a feature ?
It is not void case only but partial shipment case too.
I think it is a bug, we are looking at fixing it.
Also the case of copying completed SO to start off, the delivery flag also copied over and make it not possible to gen shipment. https://sourceforge.net/tracker/?func=detail&aid=3323648&group_id=176962&atid=879332
I think this area is quite complicated itself, and so some bug are still hidden.