Regarding clicking likes to other designers models.
Even though i put likes to other designers models in grabcad it seems like its not clicking. like button does not turn into green color or anything.
It may depend on where you click the like button. I've seen some inconsistencies in the flag turning green or not throughout the site.
As a test, go to your icon in the upper right corner and look at "My Likes". If it is in there, then it has been liked regardless of the flag color.