Created attachment 88024 [details]
EDID (retrieved from sysfs)

Passing drm_kms_helper.edid_firmware=edid/1280x1024.bin to the kernel command
line seems to fix the problem as well.

Otput of parse-edid: 

parse-edid: parse-edid version 2.0.0
parse-edid: EDID checksum passed.

    # EDID version 1 revision 3
Section "Monitor"
    # Block type: 2:0 3:fd
    # Block type: 2:0 3:fc
    Identifier "KDS XF-70 "
    VendorName "STC"
    ModelName "KDS XF-70 "
    # Block type: 2:0 3:fd
    HorizSync 30-72
    VertRefresh 50-160
    # Max dot clock (video bandwidth) 110 MHz
    # Block type: 2:0 3:fc
    # Block type: 2:0 3:ff
    # DPMS capabilities: Active off:yes  Suspend:yes  Standby:yes

    Mode     "1024x768"    # vfreq 75.029Hz, hfreq 60.023kHz
        DotClock    78.750000
        HTimings    1024 1040 1136 1312
        VTimings    768 769 772 800
        Flags    "+HSync" "+VSync"
    EndMode
    # Block type: 2:0 3:fd
    # Block type: 2:0 3:fc
    # Block type: 2:0 3:ff
EndSection