Spacebar as a keyboard control blocks mouse movement on some touchpads

I noticed this section in the manual:
```
KEYBOARD CONTROLS
The following keyboard actions can be used during selection:

Escape Cancel the selection and exit slurp

Space If currently making a selection, while space is held down, move the entire selection rather than change the selection's size as you move the pointer.

Shift Experimental. If the -a option wasn't specified, then set the aspect ratio to 1:1 while shift is held down, releasing it restores the un-constrained aspect ratio. Note: This behavior may change in the future depending on feedback.
```
However, on my computer, with the default input options, pressing keys such as space disables mouse movements.
This is not the case with modifier keys such as Shift, Control or Alt, so the Shift shortcut is usable.

I suggest using Alt instead of Space to fix this problem.