Repository: mne-tools/mne-python

Issue:
plot_projs_topomap() of data with EEG projection creates "EEG-style" topoplots even for MEG data
#### Describe the bug
Plotting SSP projectors via `Raw.plot_projs_topomap()`, we noticed that -- in some situations -- the visualized MEG fields didn't look quite right, i.e., looked like circular EEG topomaps instead like the expected "helmet-shaped" topomaps. Turns out, this only happened when among `info['projs']` was also an EEG average reference projector.

#### Steps to reproduce
```python
import os.path as op
import mne
from mne.datasets import sample

data_path = sample.data_path()
raw_fname = data_path + '/MEG/sample/sample_audvis_filt-0-40_raw.fif'
raw = mne.io.read_raw_fif(raw_fname, preload=True)

raw.copy().set_eeg_reference(projection=True).plot_projs_topomap()  # Add EEG avg ref projector
raw.copy().set_eeg_reference(projection=False).plot_projs_topomap()  # No EEG avg ref projector
```

#### Expected results
MEG topomap fields should follow the MEG helmet, and EEG fields should be circular.

#### Actual results
**With EEG avg ref projector:**
<img width="502" alt="Screenshot 2020-07-10 at 18 31 14" src="https://user-images.githubusercontent.com/2046265/87178570-a204b580-c2dd-11ea-95ed-63534e333475.png">

**Without EEG avg ref projector:**
<img width="697" alt="Screenshot 2020-07-10 at 18 31 21" src="https://user-images.githubusercontent.com/2046265/87178625-b943a300-c2dd-11ea-9c3c-7810ff4c076e.png">


cc @agramfort 


Discussion:
@hoechenberger do you want to look into how to fix this? I can confirm the bug
I might have time for this tomorrow, sure. But if you're asking if I would also be okay with you going ahead: sure ;) 

Resolving patch:
diff --git a/mne/viz/topomap.py b/mne/viz/topomap.py
--- a/mne/viz/topomap.py
+++ b/mne/viz/topomap.py
@@ -342,6 +342,7 @@ def plot_projs_topomap(projs, info, cmap=None, sensors=True,
         spheres.append(this_sphere)
         outliness.append(these_outlines)
         ch_typess.append(ch_type)
+        del data, pos, this_sphere, these_outlines, ch_type
     del sphere
 
     # setup axes
@@ -383,7 +384,7 @@ def plot_projs_topomap(projs, info, cmap=None, sensors=True,
                           outlines=_outlines, contours=contours,
                           image_interp=image_interp, show=False,
                           extrapolate=extrapolate, sphere=_sphere,
-                          border=border, ch_type=ch_type)[0]
+                          border=border, ch_type=_ch_type)[0]
 
         if colorbar:
             _add_colorbar(ax, im, cmap)
diff --git a/tutorials/preprocessing/plot_50_artifact_correction_ssp.py b/tutorials/preprocessing/plot_50_artifact_correction_ssp.py
--- a/tutorials/preprocessing/plot_50_artifact_correction_ssp.py
+++ b/tutorials/preprocessing/plot_50_artifact_correction_ssp.py
@@ -15,7 +15,7 @@
    :depth: 2
 
 We begin as always by importing the necessary Python modules. To save ourselves
-from repeatedly typing ``mne.preprocessing`` we'll directly import a couple
+from repeatedly typing ``mne.preprocessing`` we'll directly import a handful of
 functions from that submodule:
 """
 


Test patch: