In 5.3.x you specified an app name and a folder to build in and it would then create appname.app in that folder -
now it all seems wrong in 5.5.1f1 - you specify a folder and if that folder is called ‘name.app’ it builds into that folder, if it has no .app extension it is built into an adjacent folder (!!) call name.app
Basically it seems to have been broken…