If first interaction with PyVista plot is a zoom action, a sphere is placed on the brain #7534
Description
Describe the bug
In the new PyVista-based viewer in 0.20, if the first interaction with the brain is "swipe up or down" on my trackpack (to zoom), a sphere is placed on the brain as if I had clicked on it. If I first click somewhere else and then start zooming, the problem does not occur.
Steps to reproduce
Plot an STC with the PyVista backend. After the window has opened, place the mouse pointer above the brain and scroll up or down.
Expected results
Zoom level should change.
Actual results
Zoom level changes and a sphere is placed on the brain.
Additional information
Screencast: https://drive.google.com/open?id=1NjRbsh1G4a8x-g9PscAqpEm3eIXkwp_P
Platform: macOS-10.15.4-x86_64-i386-64bit
Python: 3.8.2 | packaged by conda-forge | (default, Mar 23 2020, 17:55:48) [Clang 9.0.1 ]
Executable: /Users/hoechenberger/miniconda3/envs/mne-dev-new/bin/python
CPU: i386: 8 cores
Memory: 16.0 GB
mne: 0.21.dev0
numpy: 1.18.1 {blas=blas, lapack=blas}
scipy: 1.4.1
matplotlib: 3.2.1 {backend=Qt5Agg}
sklearn: 0.22.2.post1
numba: Not found
nibabel: 3.0.2
cupy: Not found
pandas: Not found
dipy: 1.1.0
mayavi: 4.7.1 {qt_api=pyqt5, PyQt5=5.12.3}
pyvista: 0.24.0
vtk: 8.2.0