Have Form with Embedded view. When the form is presented to the user w/in a frameset, the view entries auto open when highlighted instead of waiting on a true click. The same occurs if a document is checked except the default highlighted document is opened instead of the checked one.
The frame containing the form containing the embedded view had it's default target frame set to itself (as it was the main content form).
Once this was turned off and documents selected were opened as new window tabs, functionality was restored.
No true solution was found.
This "feature" has been noticed in 7.x and 8.0x and 8.50.