Could you please tell me more about your system. Specifically:
Which version of gtk3 are you using?
What are the settings (Horizontal and Vertical DPI) in edit->preferences Windows/Screen tab?

Thank you

If you open a file resave it, open it again, resave it, always without changing the window height, does the window keep shrinking? At a fixed amount?

(In reply to comment #1)
> Could you please tell me more about your system. Specifically:
> Which version of gtk3 are you using?

I'm using Debian unstable with some packages from experimental. I have gnumeric 1.12.2 and gtk 3.8.2.

> What are the settings (Horizontal and Vertical DPI) in edit->preferences
> Windows/Screen tab?

96. Changing that had no on the window shrinking.

(In reply to comment #2)
> If you open a file resave it, open it again, resave it, always without changing
> the window height, does the window keep shrinking? At a fixed amount?

Yes, the window keeps shrinking until of the cell area only the header row is visible. I took some screenshots and checked, the reduction is a fixed amount of 36 pixels.

Thank you. Your info should help us a lot. I don't see this behaviour but I do not run gtk 3.8.x.

For anyone else wondering, a good work-around is to use the -g/--geometry option, e.g. use the following as ~/bin/gnumeric or something that precedes /usr/bin in $PATH.

#!/bin/sh
/usr/bin/gnumeric -g 1400x960+260+120 "$@"

I no longer experience this using Gnumeric 1.12.18 and GTK+ 3.14.5.

Thanks for reporting back.

Feel free to reopen if the problem comes back.