screen switching, how to get rid of black intermittant sceen

In my previous sys: setup switching betwean screens (>WB & custom) was smoot. Now i get a black screen before the new screen appears.
The characteristics of both screens are the same :
resolution is the same: 1280x1024RGB
Font is the same: DejaVu Sans 18
I have ticked "As default" everywhere that can be chosen in the custom screens preferences

What am i missing?

@JosDuchIt

Bit depth (the number of colours) ? Frequencies ?

@JosDuchIt

As TSK said you should make sure that the screenmodes are exactly the same.

If there is still a delay when switching it might be that you are low on video memory and graphics.library has to page in the bitmap for the other screen before it can be shown.

@JosDuchIt
In my 'Screens' prefs, I have no Screen mode set in the 'Display' tab and the screen mode is set in most of my programs that open a screen. The 'GUI' and 'Palette' tabs have "Like Workbench" set.

@xenic

Have you changed your monitor? is it connected via VGA, DVI or HDMI?

How muich ram does your gfx card have?

Is the sofware running on the other screen old non MUI 68k stuff that's possibly doing slighlty ilegal things?

If it's not an HD card then I recommend you only use 16bit screens'

BTW. 1920x1080x32 here on a sdamsung 27" monitor and switching is instant with same mode screens.

@TSK
i use RGB16 in both cases.
The frequencies seem to be chosen automatically in screenmode prefs, and on screens prefs i don't see them anywhere ...

@xenic
I changed to "as workbench" wherever i did note the possibility.
No change yet
Quote:

I have two screens defined: Wordworth and OWB (Odyssey)
I don't see how you can not define the screen mode, or wait:
having set for the OWB screen display mode the "Apply" choice to "never" and rebooting the screen mode was empty now. Odyssey positioned itself on the WB screen though.
...
and now the miracle:

after having set the OWB screen mode again to 1280x1024RGB16, and the the Apply choice to"as default" he switching is as wanted, no black screen anymore :)

@Severin
I've used the same (VGA) monitor since I bought my first NG Amiga. I've upgraded hardware several times with each system using a different graphics card. With each new hardware, I had to change the monitor prefs in those programs that save the ModeID in their prefs. I set all my screenmodes to 16 bit because I had several programs that won't work on 32 bit screens. I could switch to 32 bit screens now but I don't know if it will be any improvement for me since I'm partially color-blind.

@Severin

My setup is the same as before my HD crash - onmy the HD has been replaced with an older 40 GB drive
The monitor is still the same too: a HP2211x connected to the graphics card DVI connector.

The only thing that may have changed is the selected resolution (if so then lower)