Please open the file attached.
Make sure that you have Bounding Box on, and Scale Corners off.

1. Select any one of the green bars.
2. Try to make it shorter or longer, using bounding box (that is grab the center marker on the a short side) — works fine.
3. Select the dark red long bar.
4. Try to transform in the same manner — and fail. The bar gets only longer, and can't be made shorter (or shorter back).
5. Make the red bar slightly wider or select the orange bar, it is a wider copy of the red one.
6. Try to make it shorter. You succeed at first.. But then it bumps into something and refuse to become any shorter.
7. Make it as short as possible, release the mouse and try to make it shorter again — and get the same behavior as in step 6!

Now enable scale corners and try to shorten bars again — now it works fine
(but corners get smaller, which is not what is wanted in the first place).