Here is the result I got :
I'ts when trying to change atari resolution to 1024x768
When keeping the default one (but, small) it seems to work fine
after checking this on Atari mailing list, this problem was in fact described in Hatari's manual :
Basically, TOS4 doesn't support extended VDI resolution ; you need to use EmuTOS for this.
A popup message has been added to Hatari to warn the user in case he uses Falcon + TOS 4 + VDI