When updating title and/or caption for multiple photos it isn’t clear whether there is existing text about to be overwritten. In both cases if all the selected photos have the same existing title or caption that text is displayed. However, if some have no title or caption, or they have different ones, the fields are displayed as blank.
I commonly have the scenario in which I have many photos with the same title but some might have a caption, some may not. If I want to add a caption to a selected few I need to visually check each one to make sure it is empty or OK to overwrite.
Apple Photos has a protection against this in that it displays ‘Various titles’ and ‘Various descriptions’ in the relevant boxes so if you enter text there you know you are overwriting something. If the existing description fields are blank it says ‘Add a description’’ and similarly if the titles are all blank it says ‘Add a title’.
In Mylio I can have 2 photos with different existing captions. If I select both it says ‘Caption this photo’ without any regard/warning for existing text.
This might be an enhancement but I’m inclined to say bug as it is misleading and potentially leads to loss of data.