If a file shows furniture with Red X, this means the Sweet Home 3D file is incorrect. Under Mac OS X until version 2.4, this could happen when you kept opened during a few days a file where you imported some furniture. I changed temporary files management in the version 2.5 and this case shouldn't happen anymore.
Morgan, before considering your case as a bug, could you tell us if the program crashed at a moment or an other, if you moved files in App.Support folder or if you transfered your file. Most users in your case have problems after a transfer with an email or an USB key.