[ubuntu_mate] HDMI works with Live Iso but not with installed OS

Hi! On a notebook the HDMI secondary display output is not working (no signal) after fresh install of UbuntuMate 16.04. It is working properly with the Live Iso from the very begiing of the boot process. Nouveau driver in use in both cases.

What may trigger this behaviour? What should I investigate or how should I proceed? Any hint will be very appreciated. Thanks.

Additional informations:

• Notebook: Compaq Presario CQ60-203EL
• External HDMI TV: Samsung LE32B530P7W
• Nvidia proprietary driver behaves in the same way not solving the issue under Ubuntu 16.04.
• Works with the very same hardware, free and proprietary driver (version 304.131) under Ubuntu 12.04.
• System update ininfluent: OS install performed without internet coection. No change with full update.
• Xorg.log files show no differences between the two boot modes: everything seems to be properly detected and configured in the same way.
• Output of "xrandr --verbose" is the very same on Live and installed OS.
• Notebook uses Fn-f4 as the toggle (switch) display key. I'm unable to confirm Fn-f4 detection: acpi_listen shows no output. However, it is not necessary to use such feature with the Live Iso where mate-display-properties and xrandr properly handle display toggling on the fly.
• Audio: Ubuntu 12.04 detects one properly functioning HDMI stereo output. Ubuntu 16.04 reports a 7.1 HDMI output in addition. When an HDMI audio device is selected under Ubuntu Live 16.04 audio gets disabled and a dummy output is reported. Therefore audio through HDMI is not working under Ubuntu 16.04 neither with Live.
• Avoiding the use of the vt.handoff kernel boot parameter or use of nomodeset does not solve the issue.
• Forcing various manual settings through xorg.conf using "NVIDIA X Server Settings" (while using proprietary driver) is noneffective: from the notebook side everything seems to be already configured and working properly except for the signal not being detected by the secondary display.
• Kern.log files differentiate between Live Iso and installed OS mainly in a few additional lines about vesafb as follows:

--- /LiveISO_Logfile/kern.log
+++ /InstalledOS_Logfile/kern.log

-Command line: file=/cdrom/preseed/ubuntu-mate.seed boot=casper initrd=/casper/initrd.lz quiet splash --- maybe-ubiquity
+Command line: BOOT_IMAGE=/boot/vmlinuz-4.4.0-21-generic root=UUID=9e0c6ddb-1b72-4d00-8b7f-3495c0844123 ro quiet splash vt.handoff=7

-RAMDISK: [mem 0x7e715000-0x7fffffff]
+RAMDISK: [mem 0x33b66000-0x35daafff]

-Kernel command line: file=/cdrom/preseed/ubuntu-mate.seed boot=casper initrd=/casper/initrd.lz quiet splash --- maybe-ubiquity
+Kernel command line: BOOT_IMAGE=/boot/vmlinuz-4.4.0-21-generic root=UUID=9e0c6ddb-1b72-4d00-8b7f-3495c0844123 ro quiet splash vt.handoff=7

-Memory: 2792464K/2881972K available (8356K kernel code, 1278K rwdata, 3920K rodata, 1476K init, 1292K bss, 89508K reserved, 0K cma-reserved)
+Memory: 2782888K/2881972K available (8356K kernel code, 1278K rwdata, 3920K rodata, 1476K init, 1292K bss, 99084K reserved, 0K cma-reserved)

-Console: colour VGA+ 80x25
+vt handoff: transparent VT on vt#7
+Console: colour dummy device 80x25

-tsc: Detected 2099.932 MHz processor
-Calibrating delay loop (skipped), value calculated using timer frequency.. 4199.86 BogoMIPS (lpj=8399728)
+tsc: Detected 2100.014 MHz processor
+Calibrating delay loop (skipped), value calculated using timer frequency.. 4200.02 BogoMIPS (lpj=8400056)

-smpboot: Total of 1 processors activated (4199.86 BogoMIPS)
+smpboot: Total of 1 processors activated (4200.02 BogoMIPS)

-Freeing initrd memory: 25516K (ffff88007e715000 - ffff880080000000)
+Freeing initrd memory: 35092K (ffff880033b66000 - ffff880035dab000)

-audit: type=2000 audit(1469294993.004:1): initialized
+audit: type=2000 audit(1469649024.116:1): initialized

+vesafb: mode is 640x480x32, linelength=2560, pages=0
+vesafb: scrolling: redraw
+vesafb: Truecolor: size=8:8:8:8, shift=24:16:8:0
+vesafb: framebuffer at 0xc5000000, mapped to 0xffffc90000800000, using 1216k, total 1216k
+Console: switching to colour frame buffer device 80x30
+fb0: VESA VGA frame buffer device

- Magic number: 8:464:492
-rtc_cmos 00:02: setting system clock to 2016-07-23 17:29:54 UTC (1469294994)
+ Magic number: 8:838:850
+ index2: hash matches
+rtc_cmos 00:02: setting system clock to 2016-07-27 19:50:25 UTC (1469649025)

+checking generic (c5000000 130000) vs hw (d0000000 10000000)
+checking generic (c5000000 130000) vs hw (c4000000 2000000)
+fb: switching to nouveaufb from VESA VGA
+Console: switching to colour dummy device 80x25

-tsc: Refined TSC clocksource calibration: 2100.000 MHz
-clocksource: tsc: mask: 0xffffffffffffffff max_cycles: 0x1e4530a99b6, max_idle_ns: 440795257976 ns
+tsc: Refined TSC clocksource calibration: 2099.999 MHz
+clocksource: tsc: mask: 0xffffffffffffffff max_cycles: 0x1e452fc488e, max_idle_ns: 440795307124 ns

-nouveau 0000:02:00.0: DRM: allocated 1920x1080 fb: 0x50000, bo ffff88007f88b800
+nouveau 0000:02:00.0: DRM: allocated 1920x1080 fb: 0x50000, bo ffff8800356e3800