I have tried make main development window to narrowest width. Attached very_narrow.png shows it works fine, and normal_size.png shows what's it looks like when maximized. It works fine on Ubuntu 64bits. My Eiffel Studio is build from SVN revision 66888.
Maybe this bug is fixed by other bugs fixing.
Could you try newer Linux Eiffel Studio to see if this bug still happen?
Thank you.