It is because of the new feature "Outliner-Properties syncing", now depending on where you click (object's name, modifier icon, object data icon, material etc.) it will automatically change the properties section. I can understand that it's a big change and can cause some troubles like this, but there are a lot of other situations where this feature actually speeds up a lot the process of dealing with multiple objects, modifiers and constraints. I'd say though that it could be good to have an option to disable it, or at least to add physics and particles icons to the outliner so that the sync happens also for them. For now, what you can do is have the properties panel not sharing an edge with the outliner (basically have the two editors detached), in that case the sync no longer happens.

Thanks for your reply. I did what you said, placing the properties somewhere else and it works, but it changes my screen config and I don't like it. An option would be great !!!

No problem. Anyway, for the future I'd suggest you to post these observations on devtalk, as here is specifically for bug reporting.

The devtalk topic where the outliner topics are discussed is here https://devtalk.blender.org/t/outliner-gsoc-feedback/15948