When you make a payment from an account it is either a transfer to another account or it is paying something like a bill, it cannot be both, hence you select either a category or an account, there is no such thing as categorizing a transfer.
Perhaps if you could explain what you are trying to do and your objective we could better advise on an approach.
My English is too poor, i put pictures to explain
I make a transfert between "caisse d'epargne" to compte courant"
if i want to choice in compte courant the categorie "xxxxxxx" the operation does'nt appear in compte courant, i dont know where is it .. i just have the 500€ less in caisse d'épargne and nothing on compte courant
I think I understand what you are doing and why you are seeing the outcomes you are.
Moneydance is built on the principles of Double Entry accounting, the basic principle is that for every Credit there must be a corresponding and equal Debit.
Categories in Moneydance are just a special type of account, in general they represent Income and Expenditure items whereas accounts represent Asset and Liability type items.
Thus to comply with the rules of double entry when you take money from a bank account you can place it into either another account or into a category, you cannot place it into both an account and a category as that would be using the same funds twice.
You do not state why you want to categorize these funds as well as transfer them between accounts, in most instances you would not be doing this, for example if you were transferring funds to a credit card you would not categorize the transfer but you would categorize the individual payment transactions made using the credit card.
If you really need to categorize the transaction then it is necessary to create a second entry in order to comply with the rules. For example the first entry may debit one and credit the category you want to use, the second entry would credit the other account and be categorized using a specifically created category for the purpose.