Not able to add color stops in linear gradient layer

[AnishGG]

Synfig version & platform:
Synfig version: master branch - 3f3c797
Platform: Ubuntu 18.04.4 LTS

Issue description:

In the gradient editor(for gradient layer), I am not able to add a color stop using two finger touch on the touchpad(right click on the mouse works). In general two finger touch is bind to right clicking in my OS. I also checked that this 2 finger touch is working on other areas of Synfig, like canvas.
Is there some key binding problem here?

[rodolforg]

AFAIK, it shows up a popup menu that pops down as soon as you release right mouse-button :/

[AnishGG]

Alright, So will this count as non Synfig issue. I mean, all that Synfig registers is release of right mouse-button and then shows up a popup menu?

Here I am attaching an image showing the area where the 2 finger touch works: