M1306B -> Supreme 20 problem

Hi all,
I have a problem with Supreme 20 and IFC command. Initial configuration looks like this:

AT&V
AT+ICF=3,4
AT+IFC=0,0
AT&D0
AT&S1
AT&C1
ATV1
AT+CMEE=0
AT&W
ATZ

After these commands:
Q:0 V:1 S0:000 S2:043 S3:013 S4:010 S5:008
+CR:0 +CRC:0 +CMEE:0 +CBST:0,0,1
+SPEAKER:1 +ECHO:0,127 &C:1 &D:0 %C:0
+IPR:19200 +ICF:3,4 +IFC:0,0

IFC=0,0 means NO flow control in both directions and CTS always high. But it’s not. It’s changes according to DTR .
Any ideas why it happens like this? My hardware uses CTS as modem present control. I can’t control DTR.

M1306B with the same configuration works ok. I did not find any info about IFC changes in delta.

Best regards