Edge_DoubleLoop_Slide_Adj/OffCenter

I just tried the Edge_DoubleLoop_Slide_Adj/OffCenter streamline basic tools and have some issues.
Because the tools are named "slide" I expected a slide that doesn't leave the limits of the surface. Just take a look at the comparison below to see what I mean:

Is this intentional?

And also: It would be better to put the alteration between even/proportional onto a hotkey other than ctrl/shift, for example caps lock or space, because ctrl/shift also controls steppings and I am not able to do proportional with steppings at the same time with these current settings.

The new feature is added.