If a clip is has audio and video, then it can be linked/unlinked, but not if the soundtrack is a separate entity.
Try this. Open a new sequence by clicking the + sign to the right of the Sequence 1 tab. Click the Sequences tab above the clip bin... 
Drag or otherwise place Sequence 1 in Sequence 2. Now in sequence 2, after splitting both A/V tracks, when one is deleted the other will be as well.
Or, export the sequence, then clear the editor and load the clip. A/V will be linked. But be aware that the exported section won't have individual clips.
The viewing problems make no sense. Close VP, relaunch and under OPTIONS | DISK tab Clear Unused Cache Files. Then load the project.
If it's still doing odd things, test the latest release.
Save Project File AS routinely, giving it a unique # or name, so as not to overwrite prior saves. Using Save Project Files (no AS) will overwrite. From the HOME tab, the AS choice is available by clicking the caret to the right of the Save Project button on the toolbar. That way you're protected, and shouldn't lose anything.