I find that if I ever try to open a M100HD project directly by double clicking that project file, M100 will launch and just take me to the previously opened project. Then it will display an error that says it could not open the project because another project is already opened.
This happen whether or not M100HD is launched already or not.
The only workaround is to old the option apple keys and cancel the new project dialog box and then navigate via the m100 finder window to open the project you want directly. Otherwise it always launches the last project you were in.