Hello community,
I did not find any solutions to solve really strange port-forwarding problem in my network. Probably somebody here knows the right way to solve it.

My network:
I have 2 Router-cascade with DMZ-zone.
The first router has a DSL-modem function and a connection for the USB-Printer (IP-pool aa.aa.aa.0/24). USB- Printer can work with TCP/IP and 9100 port RAW. (aa.aa.aa.1 port 9100).

One LAN cable connects the first port with Mikrotik 2011 (WAN connection on Mikrotik).
Mikrotik has two networks bb.bb.bb.0/24 with bb.bb.bb.1 gateway and cc.cc.cc.0/24 with cc.cc.cc.1 gateway). All computers and routers have static IP's.
NAT rules: masquerade from Mikrotik networks to WAN interface and few DST-NAT rules for the Storage drive in the cc.cc.cc.0/24 network from the DMZ side. Everything works fine, I have internet connection can ping the first router aa.aa.aa.1 can use a web server and so on.

At the same time I can not print any documents with standard winprint function by windows 7. It seems, that my PC (IP bb.bb.bb.123) can not get a response from the first router with connected printer (aa.aa.aa.1 port 9100). I tried everything, checked traffic with Wireshark and Torch, made additional DST-Nat rules from the first router to the PC nothing helps.
Strange behavior:
If I connect my PC to the first router directly, print something and after that will connect my PC to Mikrotik again- everything will work properly and I can print everything even without DST-NAT rules. After PC reboot it does not print again.

What I ve recognized:
-The first router see only the Mikrotik IP address.
-Torch did not show me any direct connections from PC to the First Router. Only PC- external IP address from Mikrotik.
-WINPRINT uses each time a different port from 20000-65000 pool (wireshark info).

I tried everything, with firewall rules for established connection and without. Nothing helps.
Probably, somebody here knows this strange behavior and can help me.

Kindly regards and Happy New Year,