When using approval tasks we modify the approval form to show the related item data in the approval form by following this guide: http://projectpoint.at/how-to-context-item-data-in-infopath-approval-forms/
However, this only seems to work when using a list workflow. In case it is a Site Workflow which triggers the approval task this doesn't work as the 'WorkflowItemID' seems to be empty or different to the 'ItemID' and therefore the filtering in the InfoPath data connection doesn't work.
Does anyone have a solution or an idea how this can be solved? I was thinking about querying the list where the related item is saved to get the ItemID of the related item but i don't have a clue how to get this to the InfoPath form to use it as filter for the data connection.