There seems to be inconsistencies in mathematical expressions that create MatExprs.

System information (version)

• OpenCV => 4.1.0
• Operating System / Platform => macOS 10.13.6
• Compiler => clang-1000.11.45.5

Detailed description

I have been trying to use opencv to do some image processing, and I have found an inconsistency between using Mat and MatExpr.

Steps to reproduce

Specifically, in the following code, I would expect the output in both cases to be the same:

Mat m(1, 1, CV_32FC3, 1);
Mat n = m.clone();

Mat temp = m * 5;
temp = temp + 10;
std::cout << temp << std::endl;

Mat temp2 = n * 5 + 10;
std::cout << temp2 << std::endl;

However, the output I get is:

[15, 0, 0]
[15, 10, 10]

There have been some similar previous issues (#9688 #9720), but those are both a bit older, and I am not sure they show the same issues.