>> The doc-string of `window-min-height' states
>>
>> *Delete any window less than this tall (including its mode line).
>> The value is in line units.
>>
>> Hence it's certainly not a bug.
>
> I am not sure I agree. It does not say under what conditions it can
> delete that window.
It may happen whenever you create or resize any window on the associated
frame as I understood from the code. The doc-string doesn't help much
in this sense - you simply have to wait for the worst :-(
> I think the conditions should be specified in the doc string. And I do
> not think that the conditions should embrace the case with ediff. There
> is simply no need to delete that window during resizing.
That's what `window-min-height' is for. Setting it to 2 globally should
avoid that any window with a modeline gets deleted during resizing.