I actually had 2 of those attached to a button,
one acting on the button itself and another one acting on another button.
I ended up to have some strange case where the scale of one button ended up to be zero.
It was happening when the he button was disabled using an anim (much like in example 3 with menu transitions)
After a few debug log i believe I found the issue, In UIButtonScale Script line 31 I added the text in blue:
if (tweenTarget != null && mInitDone)
As this bug was not always happening I seems to have fixed the issue but i can't tell for sure still...