Exploring the post here , I created an example where parallel sequence flows were merged at an activity "uncontrolled flow". However that activity only operates once. However, Page 115 of the BPMN 1.1 spec states
If the multiple incoming Sequence Flow are actually parallel instead of alternative, then the end result is different, even
though the merging configuration is the same as Figure 10.29. In Figure 10.30, the upstream behavior is parallel. Thus,
there will be two Tokens arriving (at different times) at activity “D.” Since the flow into activity “D” in uncontrolled,
each Token arriving at activity “D” will cause a new instance of that activity. This is an important concept that modelers
of BPMN should understand.

My understanding from the spec is that a task/activity with a uncontrolled merge of two or more parallel paths should result in multiple execution of the task depending on the number of process tokens that reach it. The Intalio implementation appears to create an implicit gateway sync and only execute the activity once. (see the example in the referenced post)

regards
David