Hi Andrés,
Scripts are always executed from existing disk files, never from source code in memory. Before running a script from the Script Editor window, PI first verifies that the version that you have in the editor is either current or newer than the corresponding file. If the document has been newly created, you are asked to save it before execution. If the document has been previously loaded from or saved to a disk file and it has been modified, it is saved automatically before execution. However, if the existing file has been modified outside of PixInsight's editor, we have a risky situation: you are about to overwrite a newer version generated by an external application, and most likely you're doing so inadvertently.
In previous versions of PixInsight, when an editor file was modified by an external application, PI notified you immediately with a message box. This was causing problems with spurious filesystem notifications and multiple file change events, especially on Mac OS X. In the new versions, external modification events are captured and filtered in a robust way, and are never notified "aggressively" (just by changing the file item icon to a warning sign). The decision to either reload or overwrite an externally modified file is postponed until the necessity arises. This strategy is much more efficient and secure.
In the final 1.8.0 version, attempting to execute an externally modified script is not allowed. You have to either reload it, or save it before execution. The purpose of all of these limitations is to prevent accidental losses of source code.
