No bug here, just normal behavior. This happens because you have the strict file save mode option enabled (it is enabled by default).
When you save an image in PixInsight, some formats and/or format options may prevent some properties of the image from being correctly generated or represented in the saved image file. The most obvious example of this is when you save an image in the JPEG format. Since JPEG uses a lossy image storage scheme, what is saved as a JPEG file does never represent the true contents of the original image. A not-so-obvious example is saving an XISF image in FITS format. Since FITS is unable to store and represent most of the advanced features of XISF (image properties, Unicode textual information, advanced metadata such as display functions, RGB color spaces, etc.), you almost always lose some data when you open an XISF image and save it as FITS. When this happens and the strict file save mode option is enabled, PixInsight does not associate the saved image window with the generated disk file. It does that because the generated file does not store all of the existing data and properties of the image.
You can disable the strict file save mode as follows:
- Select EDIT > Global Preferences
- On Preferences, select the File I/O Settings section.
- Uncheck the Strict file save mode option.
- Press F6 or click the Apply Global button.
