If you create a lookup field (in FORM_B), and within the definition of that lookup, you enable :
Display Type = Dropdown
and also select :
When you then use FORM_B, and use the link on the field, to generate a new record in FORM_A, once saved, that entry does not get sorted in alphabetical order in the drop down list.
Only by exiting the form and re-selecting the form, does the correct behaviour occur (alpha sorting).
Not a major issue, but shoudl be looked at to resolve the dynamic sorting.