Hi Doss and John,
I had a careful look and it appears that when on the Settings page, under Views, "Show images in month view" is not checked, then in the hover box with event details, thumbnails are shown next to each other, which is fine. However, if "Show images in month view" has been checked, in the day cells in Month view the images are shown under each other.
Don't ask me why
To solve this, edit the file "views/month.php" and
change line 49 from . . .
foreach ($imgs as $img) { echo $img[0]."<br>"; }
to . . .
foreach ($imgs as $img) { echo $img[0]; }
In other words: delete ."<br>"
Now the thumbnails will be shown in line (if they are not too wide and fit).
Roel
PS. I will change this is the next calendar version.