Intensity change after select panels

[Mava04]

Hi,
I am using LSM Toolbox v4.0g in Fiji v1.53i on both Windows 10 and Mac Big Sur. When making a montage from a RGB image and using the Select Panels tool to overlay 2 panels by copy-pasting, I have different outcomes on Windows and Mac:

• on Windows, it works: the intensity of the pasted image in the overlay corresponds to the original one in the panel;
• on Mac, the intensity of the pasted image is higher in the lower half (or quarter, not predictable) of the overlay. This is visible after clicking once anywhere on the image.

Please find attached 3 example images generated on Mac:

1. Montage of MAX = montage before using the select panels tool
   

2. Montage of MAX_beforeClick = make montage, select panels, cmd+c, cmd+v for the green panel, before clicking
   

3. Montage of MAX_afterClick = make montage, select panels, cmd+c, cmd+v for both panels, after clicking.
   

Where does this come from? Any quick fixes?
Thank you in advance

Martina