3d plots flattened when printing to file

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When I print to file using The Sage Notebook (flask) - clicking the print option and then printing to file using CUPS - everything is displayed correctly except plot3d plots which are squeezed to have a height of a few centimeters while the width remains the same. I do not have the same problem with other types of plots like "plot" or "countourplot". I do not know whether this has anything to do with my screen being 4k, but it reminds me of similar picture scaling issues I have with maple.

What I get: https://s17.postimg.org/d3q80qlf3/scr...

What I expected: https://s17.postimg.org/72sj3vokv/scr...