Problems getting Multiple Items tab to work

Every month I pay Plusnet by direct debit. The bill can be divided into internet and telephone.
I follow the instructions in the support guide "How to explain a receipt on an imported statement with multiple items" but still cannot get it to work.

I do the following:

1. Navigate to Money>Banking
2. Click on the imported statement
3. Click on a receipt to begin explaining
4. Use the multiple items tab and explain the first item
5. Click on the Add Transaction button
6. Explain other items by repeating steps 4 & 5

7. Hit the Add Transactions to complete

   Everything goes well up to number 6. I manage to add the first transaction (e.g. the element of the bill I want to assign to 'internet') but when I click the "add transaction" for the remaining amount (the 'telephone' element of the bill), Clearbooks just links back to my imported statement and nothing has happened. Am I missing something obvious here? Is it because both of my items are to the same entity? Any help appreciated!
   Richard