There can be several ways for this to happen
- A new bgl file needs to be saved in the Addon Scenery Folder Structure and needs to be in a scenery sub folder
- The scenery folder needs to be active in FS
- You have FSX open and are at the airport you are modifying. If you have already saved the Bgl one or more times then FS will have locked it while using it. BglComp will not overwrite it. However neither will it give you any warning that the file is not being updated. Thus it appears that all is well but in fact your changes have not been made available to FS. A future version of ADE will address this.