bug#60015: 29.0.60; multi-line messages truncated in non-selected minibuffer

[Juri Linkov]

>> 1. (run-with-timer 5 5 'message "abc\ndef")
>> 2. then activate the minibuffer and switch back to the original buffer
>> 3. after some time observe that only the first line of the multi-line message
>>    is displayed in the minibuffer
>
> Doesn't happen here (I waited for 2.5 minutes).  Is the recipe
> complete and exact?  Does it perhaps matter how do you "switch back to
> the original buffer"?  (I used a mouse click.)

It's essential to ensure that the height of the minibuffer/echo area
initially is not more than 1 line.  Otherwise, when it's already resized
to fit multi-line messages, then all lines are displayed.

> When the problem happens, what do you see in *Messages*?  Anything
> other that "abc\ndef"?

Only the first line "abc" is displayed in the minibuffer
as the minibuffer message.