Weight Gradient and X-Mirror doesn't work together.

I tried to weight paint using the blender for the first time today.

I was pretty ecstatic when I used the weight gradient feature.

However, I was disappointed to realize that this feature did not work with the X-Mirror option.

But X-Mirror works well when I brushing.

Is the combination of weight gradient and X-mirror missing in the current version of Blender?

Or are there other prerequisites I do not know?

If it is missing, will it be improved in version 2.8?

Thank you advance.