bug#16028: 24.3.50; Latest build completely breaks my thumnail frames code

[martin rudalics]

>> What do you get here?
>
> ;; (enlarge-font-by 4)
>
> -outline-Courier New-normal-normal-normal-mono-17-*-*-*-c-*-iso8859-1 (80 . 37) 
(841 . 740) ->
> -outline-Courier New-normal-normal-normal-mono-21-*-*-*-c-*-iso8859-1 (80 . 
37) (1087 . 851)
>
> ;; (enlarge-font-by -4)
>
> -outline-Courier New-normal-normal-normal-mono-21-*-*-*-c-*-iso8859-1 (80 . 37) 
(1087 . 851) ->
> -outline-Courier New-normal-normal-normal-mono-17-*-*-*-c-*-iso8859-1 (80 . 
37) (841 . 740)
>
> ;; (enlarge-font-by -4)
>
> -outline-Courier New-normal-normal-normal-mono-17-*-*-*-c-*-iso8859-1 (80 . 37) 
(841 . 740) ->
> -outline-Courier New-normal-normal-normal-mono-13-*-*-*-c-*-iso8859-1 (80 . 
37) (677 . 592)
>
> ;; (enlarge-font-by 0)
>
> -outline-Courier New-normal-normal-normal-mono-13-*-*-*-c-*-iso8859-1 (80 . 37) 
(677 . 592) ->
> -outline-Courier New-normal-normal-normal-mono-13-*-*-*-c-*-iso8859-1 (80 . 
37) (677 . 592)
>
> ;; (enlarge-font-by 4)
>
> -outline-Courier New-normal-normal-normal-mono-13-*-*-*-c-*-iso8859-1 (80 . 37) 
(677 . 592) ->
> -outline-Courier New-normal-normal-normal-mono-17-*-*-*-c-*-iso8859-1 (80 . 
37) (841 . 740)

So what am I missing?  `enlarge-font' seems to work as expected.

martin