Nut upsdev - May 2012 - liebert-esp2 - DTR is continously asserted

Hallo list,
I encounter following problem using the liebert-esp2 driver with my 
Liebert GXT2-3000RT230:
I use a standard serial cable with all pins connected, not a cable with 
only pins 2,3,5 connected as mentioned in the ups-manual.
The UPS uses pins 4 and 6 in a special way (Pin 4(DTR) asserted 
invokes the shutdown timer when ups is on battery, pin 6 to 
ground-->any-mode shutdown).

Is it possible to make DTR continously non-asserted or must I cut the 
wire or build a custom cable?
Since the DTR signal is continously asserted, the ups will shutdown 120 
seconds after a powerfail, even if the power gets restored in this time.

I tried stty commands with no luck, i also tried to add 
"ser_set_dtr(upsfd, 0);" into upsdrv_initups() without success.

thanks for help or tips,
Paul

some information:

statserial:
Device: /dev/ttyS4

Signal  Pin  Pin  Direction  Status  Full
Name    (25) (9)  (computer)         Name
-----   ---  ---  ---------  ------  -----
FG       1    -      -           -   Frame Ground
TxD      2    3      out         -   Transmit Data
RxD      3    2      in          -   Receive  Data
RTS      4    7      out         1   Request To Send
CTS      5    8      in          0   Clear To Send
DSR      6    6      in          1   Data Set Ready
GND      7    5      -           -   Signal Ground
DCD      8    1      in          1   Data Carrier Detect
DTR     20    4      out         1   Data Terminal Ready
RI      22    9      in          0   Ring Indicator

upsc:
battery.current: 0.00
battery.runtime: 3540
battery.runtime.low: 120
battery.temperature: 0.0
battery.voltage: 824.0
battery.voltage.nominal: 828.0
device.mfr: Liebert
device.model: GXT2-3000RT230
device.serial: 0323000167AF491
device.type: ups
driver.name: liebert-esp2
driver.parameter.pollinterval: 2
driver.parameter.port: /dev/ttyS4
driver.version: 2.6.2
driver.version.internal: 0.03
input.bypass.current: 0.0
input.bypass.frequency: 50.0
input.bypass.voltage: 229.0
input.frequency: 50.0
input.frequency.nominal: 50.0
input.phases: 1
input.voltage: 229.0
output.current: 2.4
output.frequency: 50.0
output.frequency.nominal: 50.0
output.phases: 1
output.voltage: 230.4
ups.delay.start: 0
ups.firmware: GXT2MR15D-2K3K
ups.load: 17
ups.mfr: Liebert
ups.mfr.date: 15AUG03
ups.model: GXT2-3000RT230
ups.power: 513
ups.power.nominal: 3000
ups.realpower: 366
ups.serial: 0323000167AF491
ups.status: OL
ups.temperature: 39.5
ups.type: online

cat /proc/version
Linux version 3.1.10-1.9-desktop (geeko at buildhost) (gcc version 4.6.2 
(SUSE Linux) ) #1 SMP PREEMPT Thu Apr 5 18:48:38 UTC 2012 (4a97ec8)

nut installed with rpm:
Information for package nut:

Name: nut
Version: 2.6.2-31.10
Arch: x86_64
Vendor: obs://build.opensuse.org/hardware
Installed: Yes
Status: up-to-date
Installed Size: 4.4 MiB