If you are not able to install Matrex 1.3.5 on MacOSX, please check the article about this topic. You can download a more recent beta version of the SWT library for Cocoa here. As soon as Eclipse 3.5 Galileo will be released, I will update the setup files to use the new SWT library, which will probably solve the problem.
It should have been called 1.4 for the new features it contains, but when the coding started it was called 1.3.5 and so it remained. As the notes that come in the setup file report, these are the new features: