In regards to the previous statement "If you have a combination of "and" and "or" conditions, I think InfoPath won't split it to respect the possible complexity of the condition's logic.", Infopath does split the rule and that is my exact problem. I don't just think InfoPath will split the rule, I have tested this and it does occurr. I am using an InfoPath 2010 browser enabled form.
I created a rule called "Hide when A and B or AB".
The rule is for hiding a control, the conditions are very basic - field1 = "A" and field2 = "B" or field3 = "AB"
I put the same rule on a section and a field. I then save the form, and re-open it.
The rule on the section is split - the first rule is called "Hide when A and B or AB" and contains only the conditions field1="A" and field2="B", and the one InfoPath very kindly (not) creates is called "Rule 1" and has the condition field3= AB.
The rule on the field has not changed and still contains all three conditions.