variable.scss doesn't compile automatically with yarn theme:watch

Problem/Motivation

hi
i noticed that after executing yarn theme:watch automatic compile run as expected for any *.scss file in sub-folder(base, component, etc.) .
But if i change something in variables.scss automatic compile doesn't run .

Steps to reproduce

After generating my custom theme and later following the documentation about overriding the Varbase Media Header's height as described here :

1. i copy the default values in variables.scss of VMH module to the(append) variables.scssof the generated theme
2. Execute yarn theme:watch
3. change the height

Did not see any automatic change. I had to manually run yarn theme:build to see changes

Am i missing something, do i need to configure something or it is normal ?

Thanks