JESS: multislot accumulate behavior

(defrule VALIDATE:dataset-variables
    (page "edit-dataset.xslt")
    ?dataset <- (dataset (variables $?))
    ?errors <- (accumulate (bind ?list (new java.util.ArrayList))   
               		(?list add ?var)
					 ?list
					(dataset (variables $? ?var&:
        				(not (regexp "^[a-zA-Z_][a-zA-Z0-9_\\.]*$" ?var)) $?)))
=>
    (printout t "errors = " (?errors toString) crlf)
	(modify ?dataset
        ; TODO: set variableErrors for each variable in ?errors"
        (has-errors TRUE)))

Rules whose RHS modify facts referenced in the LHS gets fired twice which is normally not a problem but when I use accumulate it returns an empty list for the second firing. I had to declare slot-specific = TRUE in the fact's deftemplate that's being referenced to get it to work properly. Why doesn't it return the same result again?

Donald Paul Winston
[email protected]