CTS handshake problem



Yesterday I replaced a Q2406B by a Q24EX001.
The old Q2406B worked properly.
The new Q24 has some strange CTS-problems.
I connected my PC to RXD1 and TXD1, RTS1 is connected to VCC and CTS1 is monitored with an oscilloscope.

I did an AT&F (factory-reset). CTS-handshake is activated (+IFC=0,2)

After power-up CTS remains low - ok.
If I send a simple AT the modem answers OK and CTS is set to high - indefinitely.

But the modem still reacts on commands and sometimes (not reproducible) CTS returns to low.

If I just ignore CTS everthing works fine but I lose some data during GPRS-transfers.

So - what can I do?