The newer method is to use Enter customer payments which collects all of the necessary steps into one streamlined form.
One major problem with this form is that it allows the Payment date to be changed in cases where it should not be allowed. For example, once settlements are selected, if any of those settlements include cash discounts or exchange rates, then changing the Payment date should no longer be allowed, and this is exactly how the Customer payment journal works.
The code responsible for this decision is found at Tables\LedgerJournalTrans\isDependantOnSettlement(), and a convenient remark explaining the behavior can be found there.
/// This dependency pertains to transaction date, cash discount, and exchange rates. It is used to
/// determine whether the user should be able to change the transaction date of a journal line.
This actually makes good sense. Both cash discounts and exchange rates are date dependent, and so changing the transaction date of the customer payment after settlements are marked could be problematic at best.
The easy fix is to disable the date field altogether on the form, until a more comprehensive fix can be developed or until one is distributed from the product team. An example of disabling the field is shown below, by setting allowEdit(false) for the TransDate field in the LedgerJournalTrans data source init method.