Strange behaviour with partial evaluation and sum() function

Question

Hi all, I have encountered strange behaviour when using partial evaluation with the sum() function. 
 I get different answers with the same calculation. 
 Please see the attached screenshots to see what I mean. 
 This expression produces an incorrect result of 5. 
 
 Where this expression produces the correct result of 6. 
 
 Both expressions use the same sum(1, _)(2, 3) function. 
 Any ideas why the results are different? 
 
 Thanks, 
 Morn&eacute;

Mike Schmitt · Answer

I haven't seen this before (don't use partial evaluation much outside of apply()), but it looks like in this case the value: parameter ignores the initial input into the partially-evaluated function. 
 Thus this code: 
 a!textField(
 value: concat("mike ", _)("ok1 ", "ok2 "),
 readOnly: true()
) 
 which when run in an expression rule editor returns "mike ok1 ok2", drops the "mike" part when used as the value: parameter of the text field.