red51 - report sent. I missed to add some additional information though.
I noticed that the issue only comes up when i move a block of the same shape as is already in the active slot of the toolbar.
Example:
I have a regular square block or material 400 in my hotbar and select it as active. Then i use TAB to open the inventory and use the mouse to move a regular square block of material 200 into the active slot. The result is as described above - the block 200 gets properly placed into the active slot but on the upper right corner and in my hand its still showing block 400.
When i do the same thing with i.e. column 200 the block in my hand and in the upper right corner get properly updated