Activities arranged weirdly hierarchically in "Referenced Behavior" selection

[YaronS]

Hello,
I've set up a class with three operations and three Activities defined in it, all at the same hierarchical level underneath the class element.

If I try to set one of the Activities as the Behavior for one of the operations:

• If I do this by right-clicking on the operation, going to Properties, then going to Behavior and clicking the "Element" button, it shows me a selection tree that makes sense (that reflects the actual model tree), and I can choose any of the Activities as the Behavior of the operation.
• If I do this by just going to the "Properties" pane, to the "Referenced Behavior" property, and clicking on the "..." next to it, it shows me the Activities arranged in a somewhat arbitrary hierarchy relatively to each other (the three of them comprise a 3-level nested tree of "subtypes"). I can still choose any of them as the Behavior for the operation.

Any idea why that happens in the second case?

If I could figure out how to post images here I would.

Thanks!