In a Windows multiple-selection listbox, such as the right pane of Explorer when it displays a list of files or directories, the keyboard focus and selection are two separate concepts.
When a listbox has the keyboard focus, either a single element is outlined with a dotted rectangle - the element with the focus - or no elements at all.
Independently of that, zero or more elements may be selected. These elements are highlighted with a fill color.
You can use the arrow keys to navigate through the list, and both the selection and keyboard focus track together. Similarly, if you start typing, the selection and keyboard focus jump to a matching name. In both these situations, there is a single item selected, the same one that has the keyboard focus.
Or you can use Ctrl+arrow to navigate, which moves only the keyboard focus without changing the selection. Then you can use the spacebar to toggle the selection on the element with the keyboard focus, either adding it to or removing it from the set of selected elements.
In Parallels, these spacebar presses also pop up the OSX Quick View panel.
In this situation you can alternatively use Ctrl+spacebar, which does the same thing but doesn't trigger the popup. In fact that's as convenient as plain spacebar, or maybe even more convenient because you can just hold down the Ctrl key the whole time and use the arrow keys and spacebar to navigate and select.
So where does it become a problem? Try this:
Use Windows+E or any other method to open an Explorer, navigate to This PC, and in the right panel double-click the C: drive or any drive.
Note that there is now no keyboard focus rectangle in the right panel. Imagine the first item listed is a directory and you want to open that directory with the keyboard.
The Enter key at this point does nothing.
You can use the down arrow, but it focuses and selects the second item in the list.
You can type the letter that the first directory name begins with, but if there are two or more directories beginning with that letter, this also selects the second one.
The easy and reliable way to select the first directory is with the spacebar. And now you can use Enter to open that directory.
For whatever reason, I seem to often be in a situation where I want to navigate into a series of nested directories where the first directory is the one I want. It's very convenient to start typing spacebar, enter, spacebar, enter, etc.
Of course Ctrl+Spacebar also works without opening the OSX popup. But it's not exactly the same as Spacebar - it toggles the selection instead of always selecting.
And we're talking about 20-30 years of muscle memory - I've been using the spacebar, enter, spacebar, enter sequence ever since the earliest days of Windows. It's always worked on physical machines, in VMware, and in Parallels... Until Parallels 11 broke it.
Of course it's perfectly understandable that you weren't aware of this spacebar behavior! Probably only a small minority of users are aware of it. For those of us who do, it's pretty annoying to see that popup every time.