with the proprietary driver

Code:
xrandr --newmode "720x576_50i" 26.57 720 736 808 896 576 577 580 593 -hsync +vsync interlace
xrandr --addmode default 720x576_50i
xrandr --output default --mode 720x576_50i
X Error of failed request:  BadMatch (invalid parameter attributes)
  Major opcode of failed request:  156 (RANDR)
  Minor opcode of failed request:  7 ()
  Serial number of failed request:  15
  Current serial number in output stream:  16
it's the same with 1080i

and if I set them in the xorg.conf they don't appear in xrandr

Code:
ModeLine       "1920x1080_50i" 141.45 1920 2032 2232 2544 1080 1081 1084 1112 -hsync +vsync interlace
ModeLine       "720x576_50i" 26.57 720 736 808 896 576 577 580 593 -hsync +vsync interlace

I tried with dynamic twin view disabled and enabled and it doesn't work

I need to be able to switch them with xrandr because I want to do a tool that choose a refresh rate and resolution according to the video stream of a video player.

the mode lines are generated with

Code:
gtf 720 576 50
I tried with a refresh rate of 25 too

mirak@vdr-box:~$ gtf 720 576 25
Code:
  # 720x576 @ 25.00 Hz (GTF) hsync: 14.62 kHz; pclk: 11.70 MHz
  Modeline "720x576_25.00"  11.70  720 696 760 800  576 577 580 585  -HSync +Vsync

mirak@vdr-box:~$ xrandr --newmode  "720x576_25"  11.70  720 696 760 800  576 577 580 585  -HSync +Vsync 
mirak@vdr-box:~$ xrandr --addmode default 720x576_25
mirak@vdr-box:~$ xrandr --output default --mode 720x576_25
X Error of failed request:  BadMatch (invalid parameter attributes)
  Major opcode of failed request:  156 (RANDR)
  Minor opcode of failed request:  7 ()
  Serial number of failed request:  15
  Current serial number in output stream:  16
mirak@vdr-box:~$ xrandr --output default --mode 720x576_25
X Error of failed request:  BadMatch (invalid parameter attributes)
  Major opcode of failed request:  156 (RANDR)
  Minor opcode of failed request:  7 ()
  Serial number of failed request:  15
  Current serial number in output stream:  16
mirak@vdr-box:~$ xrandr --newmode  "720x576_25i"  11.70  720 696 760 800  576 577 580 585  -HSync +Vsync interlace
mirak@vdr-box:~$ xrandr --addmode default 720x576_25i
mirak@vdr-box:~$ xrandr --output default --mode 720x576_25i
X Error of failed request:  BadMatch (invalid parameter attributes)
  Major opcode of failed request:  156 (RANDR)
  Minor opcode of failed request:  7 ()
  Serial number of failed request:  15
  Current serial number in output stream:  16