Yah, kind of a bummer. Here's the deal:
- We originally had it working in the Tech Preview of Fusion 8
- We found that it was extremely fragile in a high number of configurations
- We made the call not to release this feature in Fusion 8 because it wasn't what we think our users expect from us.
- With 7.1.3. we just backported that logic.
It seemed to work fine in single-display (i.e. on a MacBook Pro or iMac not connected to any extra displays), but as soon as another display is introduced "bad things happen".
On a technical level, the feature works by adjusting the display topology. This is why most apps don't need to think about it, they'll just render no matter what the resolution is. It is as if the display is being physicslly 'split' into two discrete monitors/displays.
Fusion, on the other hand, really makes use of resolution information to correctly render the guest OS, and in normal life this doesn't change often. When it does, we can detect it and 'do the right thing'. Split View doesn't follow this behavior, so we don't know about a resolution change the same way we do when a monitor is plugged in.
As such, when extra physical displays are introduced, depending on their layout, the logic that Split View uses can create 'holes' in the display topology, and we are unable to detect what the correct display topology should look like.
"Bad things" include little things like VM's drawing in to display windows that don't exist, to big things like Fusion crashes.
We're working on it tho.