A multi-value parameter with post-processing function CSVTEXT() is turned into a regular string. Unfortunately this string parameter cannot be passed to a Kettle Datasource. Instead of the parameter string, a string array or java object is passed in and converted to a string using .toString().
A workaround that seems to work is to create a copy of the original parameter with formula =[original_parameter] and use this to pass down to kettle.
Attaching minimal samples. Please see screenshots for the defect and expected result.