@Tom Lahau - I think I know the scenario you are describing and have often been confused/annoyed by it, but just continued on with the task at hand. Now that you're bring it up, let's get to the bottom of it.

Is this the scenario?

1. You select an object

2. Holding down Ctrl/Cmd, you select a second object to form a group

3. You stop holding down/depress the Ctrl/Cmd key

4. You move your selected group of objects to another spot on the board using a click and drag

5. Once they are moved and you have depressed the mouse button, the objects are still selected (this is expected)

6. Now you go elsewhere in the board and select a single object and this object becomes the third selected object in your group created in step #2, even though you weren't holding down the Ctrl/Cmd key (which is unexpected)?

Is that's what happening?

And, if yes, have you (and I) really stopped holding down the Ctrl/Cmd key....?

Yes! that’s the situation . In 6 there is a small nuance (probably only in my head & that of my colleague).

Between 5 en 6 I  physically let go of crtl/cmd, then click and drag again while holding ctrl/cmd  again and drag multiple post its to make a separate new group. 

From a computers point of view I didn’t really “stop”  holding down crtl/cmd from although physically I did let go. 

So I really did let go for a second :-)

@Tom Lahau - Ahhh. Well, the computer does see that you let go of the Ctrl/Cmd key, but the objects were still selected on the Miro board. I would say that Miro’s choice to keep the objects in “selected” mode after you have moved them is standard behaviour, e.g., selecting two shortcuts on my Windows home screen and moving them, and is therefore not a bug.

You will need to continue to de-select them by pressing Esc, clicking on a blank spot on the board, selecting another object while not holding down Ctrl/Cmd, etc.