For a picture with a description already defined in the Semantic Information pane, the act of editing the EXIF metadata will cause the description in the Semantic Information pane to be lost when the application is next loaded.

Reproducible: Always

Steps to Reproduce:
1. Choose a folder with some pictures which have already been given a description in the semantic information pane.
2. Choose one of the images, view it, select <Plugins><Images><Metadata><Edit all metadata>
3. In the <Edit EXIF> tab under the <Caption> item if the <Caption:> checkbox is not ticked, tick it and then edit the contents of the caption text below the checkbox.
4. Click <OK> and quit the application.
5. Restart Gwenview and navigate to the same image.
6. The Description in the semantic information pane will have been lost.
Actual Results:  
The Description in the semantic field was no longer there so it had to be re-entered after which it stayed in place until the metadata was next edited.

Expected Results:  
Editing the metadata should not have altered the semantic information fields.

Why not return to linking the caption information in the metadata to the displayed description. This has the added advantage of carying the description of the image with the image should it be moved to another location.
I assume that what has happened is that the editing of the image contents has "moved" it in the "eyes" of the semantic information tool (tool used with as many meanings as you wish).
I fear that this is another ramification of the use of the Nepomuk/Strigi/Akonadi triumvirate and that the fault may lie in the way that the semantic data connects with a file.