[Sony Ericsson Xperia Mini, Mini Pro, Xperia Pro, A] datumdatzgr:
Solution!

An intensive research yielded the solution.

"/system/usr/keylayout/pm8xxx-keypad.kl" file has all the information about which keys will wake the phone up and which keys don't.

Originally it was:

# file pm8xxx-keypad.kl
# this corresponds to kernel/arch/arm/mach-msm/keypad-iyokan.c
#
# defines for values are in frameworks/base/include/ui/KeycodeLabels.h

# KEY_VOLUMEUP, KEY_VOLUMEDOWN
key 115 VOLUME_UP WAKE
key 114 VOLUME_DOWN WAKE

# KEY_MENU, KEY_HOME, KEY_BACK
key 139 MENU
key 102 HOME WAKE_DROPPED
key 158 BACK

# KEY_CAMERA, KEY_CAMERA_FOCUS
key 212 CAMERA
key 528 FOCUS

key 108 DPAD_LEFT WAKE_DROPPED
key 103 DPAD_RIGHT WAKE_DROPPED
key 105 DPAD_UP WAKE_DROPPED
key 106 DPAD_DOWN WAKE_DROPPED

key 16 Q WAKE
key 17 W WAKE
key 18 E WAKE
key 19 R WAKE
key 20 T WAKE
key 21 Y WAKE
key 22 U WAKE
key 23 I WAKE
key 24 O WAKE
key 25 P WAKE

key 30 A WAKE_DROPPED
key 31 S WAKE_DROPPED
key 32 D WAKE_DROPPED
key 33 F WAKE_DROPPED
key 34 G WAKE
key 35 H WAKE
key 36 J WAKE
key 37 K WAKE_DROPPED
key 38 L WAKE_DROPPED

key 44 Z WAKE_DROPPED
key 45 X WAKE_DROPPED
key 46 C WAKE_DROPPED
key 47 V WAKE_DROPPED
key 48 B WAKE_DROPPED
key 49 N WAKE_DROPPED
key 50 M WAKE_DROPPED

key 40 APOSTROPHE WAKE_DROPPED
key 51 COMMA WAKE_DROPPED
key 52 PERIOD WAKE_DROPPED
key 57 SPACE WAKE_DROPPED
key 14 DEL WAKE_DROPPED
key 28 ENTER WAKE_DROPPED
key 56 ALT_LEFT WAKE_DROPPED
key 42 SHIFT_LEFT WAKE_DROPPED

key 26 AT WAKE_DROPPED
key 27 GRAVE WAKE_DROPPED

key 127 PICTSYMBOLS WAKE_DROPPED
key 368 CAPS_LOCK WAKE_DROPPED

As one can realize, the keys with "WAKE" or "WAKE_DROPPED" labels wakes the phone up. So i deleted the "WAKE" labels of all the buttons of slide-out keyboard with root browser. Then the new form is like this:

# file pm8xxx-keypad.kl
# this corresponds to kernel/arch/arm/mach-msm/keypad-iyokan.c
#
# defines for values are in frameworks/base/include/ui/KeycodeLabels.h

# KEY_VOLUMEUP, KEY_VOLUMEDOWN
key 115 VOLUME_UP WAKE
key 114 VOLUME_DOWN WAKE

# KEY_MENU, KEY_HOME, KEY_BACK
key 139 MENU
key 102 HOME WAKE_DROPPED
key 158 BACK

# KEY_CAMERA, KEY_CAMERA_FOCUS
key 212 CAMERA
key 528 FOCUS

key 108 DPAD_LEFT
key 103 DPAD_RIGHT
key 105 DPAD_UP
key 106 DPAD_DOWN

key 16 Q
key 17 W
key 18 E
key 19 R
key 20 T
key 21 Y
key 22 U
key 23 I
key 24 O
key 25 P

key 30 A
key 31 S
key 32 D
key 33 F
key 34 G
key 35 H
key 36 J
key 37 K
key 38 L

key 44 Z
key 45 X
key 46 C
key 47 V
key 48 B
key 49 N
key 50 M

key 40 APOSTROPHE
key 51 COMMA
key 52 PERIOD
key 57 SPACE
key 14 DEL
key 28 ENTER
key 56 ALT_LEFT
key 42 SHIFT_LEFT

key 26 AT
key 27 GRAVE

key 127 PICTSYMBOLS
key 368 CAPS_LOCK

AND THE PROBLEM HAS GONE AWAY...

I attach the file you can use. But it may be specific to CM11 rom! Be careful.

A further info:

WAKE: The key should wake the device when it is asleep. For historical reasons, this flag behaves in the same manner as WAKE_DROPPED below.

WAKE_DROPPED: The key should wake the device when it is asleep but the key itself should be dropped when the wake-up occurs. In a sense, the key's action was to wake the device, but the key itself is not processed.

Again verry sorry for off-topic, but it maybe helpful for the mk16i owners, or the ones wanting to use other buttons to wake the phone up.

Thanks...