Here is an update about the bug I mentioned.
I am indeed using the latest version. But I found something else.
If I use the program in the original window size as choosen by the program, it works well. But if I maximise the window to full screen, I can't add any component to the last column on the right, for width sizes of 20, 40 or 60. But it works for width sizes of 19, 21, 39, 41, etc...
So the reason I thought it was not working only with a width of 40 is because I was not maximising the window for width of 20, but I had to do it for a width of 40.