TOPIC:

Did your system change? Please give more information!
e.g. did you update joomla? In one other case I encountered a problem with new Joomla 3.5.1 and preparing thumnails.

EDIT:
the thumbnails from earlier uploaded events are normal?It seems there are differences!
Please give more informations to reproduce the problem.

Yes I upgraded to 3.5.1. Is this going to be the issue? Should I upload the images again or is there another way to regenerate the thumbnails easily?

EDIT:
Reset and reselected image. Still elongated.

you're working with which browser?
EDIT:
during upload of a new eventimage?

www.ckdev.info/ncp4/road-trips/del-norte...jrelated&layout=blog - page with module on it.

Was on Opera. Changed to Chrome and uploaded a brand new image (never been uploaded before) and viewed in Chrome. Failed. Changed to IE 11 and did the same. Failed.

I did notice something interesting though. Previously, on Opera and Chrome, when uploading an image, after the upload, it disappears from the image selected preview and you have to go and find it and reselect it to make it appear. In IE you don't have to do that - it sticks there. Who'd have thought IE could do something useful?

about IE, I thought the same
yes, I made the same experience. We will have a look. Until now we don't know exactly the problem. We are testing.
Sorry, to say that. with the coming JEM 2.1.6 I dindn't encounter this problem. (I am testing dev5).
Please look for the rights of the thumbnail images in jem/event/small! are there problems?
what settings do you have for the thumbnails?

Max height and width = 250px

Some thumbnails are 644 and some 755. One of the "misbehaving" ones was 755. I changed it to 644 via FTP (I understand from a friend this is not the best way to do it). It had no effect on the display.