Thanks for the quick response. I downloaded the latest version, replaced the NGUI files and rebooted Unity many times but nothing changes. I have simiplified the problem to only 2 sprites, one top and one bottom, anchored the bottom one to the top sprite and set the tweenheight toggle on the button's onclick function.
Explaining it it's hard for me, maybe a very simple Unity project will explain what I'm talking about, here's the link:
I would be very thankful if you can resolve this issue or explaining what I'm doing wrong or what's an alternative solution for this problem.
Thank you