Image resize

I want to add an image to my post from an external website. Usually I use img tag with size parameter, but not every pic does really resize.

Good example

[img=330x250]https://i.imgur.com/bPfg2CE.png[/img]

Everything works fine.

Bad example

I write the next code:

[img=313x250]https://i.imgur.com/eThzWBf.jpg[/img]

then press review or edit (submit) and see very big pic. If I check the code of the post, I could see the size parameter was changed to strange values (real pic's size is 1280x1024):

[img=1024x819]https://i.imgur.com/eThzWBf.jpg[/img]

If I edit post, then values reset again to the same value.

I have no idea what's difference between these two pics and why they are treated in different way, but can provide a dozen of examples with incorrect behaviour.

P.S. zotum.net hub hosts Hubzilla v3.9.3 (developer?).