I can confirm this too. What I see is that it happens when the MindManager window is not already active. The first click in the window activates MindManager, and does not select the object that is clicked on. However, if that object has another function that occurs when it is clicked, then this function is still executed.
Similar effects can be seen in other cases; for example, if you inadvertently click on a topic icon when the MindManager window is not active, then the icon toggles to the next member in the marker group, without selecting the topic - another topic in the map can remain selected. This one has caught me out many times and caused unintended edits to a map.
When working with a dual screen setup, or if the MindManager window is not maximised in a single screen setup, it is always necessary to click twice in the MindManager window to gain control - once to activate MindManager, and again to select a topic. A workaround is to always use Alt+Tab to activate the MindManager window, even if it is already in view. Simply moving the mouse over the window does not give it focus.
All that is needed here is for any click action in the MindManager window to re-assert the selected parent object before it is executed, then all of this would be avoided. So I think this should change to a bug report.