Why don't dues orders have a check box on the portal like other orders do?
The missing select all box is actually a feature related to the Default Dues Order. This can be a confusing when members are trying to pay for dues bills and they're not able to use the "select all" option on the My Orders page. This has to do with the *kind* of Order they're trying to pay, and the kind of Order is determined by the Order Source which is set on the order record.
The purpose of the Order Source is to put a person into the correct Payment process, based on the type of Order. Dues Orders need the option to edit any optional products, so they have an Order Source of "Default Dues Item" to tell the system to use the dues checkout process and allow a member to edit their contribution amount. An Order for Classes could have the "Default Class" source, and on the My Orders page you would see a link to "Complete Registration".
This is the important part - Orders with a Source cannot be paid for at the same time as orders with a different source. So, for example, you can't pay for a Dues Order and a regular Store Sales Order at the same time because the Dues Order needs its own special checkout process for editing the contribution amounts. To enforce this rule, any Order with a Source will not have a checkbox next to it on the My Orders page because it has to be paid separately from all other open Orders.
The "Order Source" for dues is really only needed when you have dues Orders with optional products because that source is what tells the system to drop a Contact into the renewal process and allows them to edit the optional amounts. If you are running dues for MLS or Key/Lockbox, which typically doesn't contain optional products like PAC contributions, you don't need to use an Order Source. If the Order does not have a Source, then it can be paid along with other Orders with a single Payment.
So, members will get an error message on the portal if they select the Pay Orders button on the left, since no order is selected. However, if they click on Pay Dues link they will be able to pay. A line could be added to your page text on the orders page if you feel that this clarification would be helpful to your members.
Members go directly to the pay dues screen if they click on the link in the blue box on the portal.