W5100 problems with delay

We are developing one project based on W5100 chip. And caught a problem with delay in TCP/IP routine maybe. When we send package by package from remote server with 100ms delay between them we getting interrupts in estimated time. But when two packages come out from server port with 1…30 ms delay between them (very close one to one) we get interrupt from W5100 with abnormal delay (100…200 ms). Can you help me find what is wrong with our solution?
Thanks a lot.

Verify that you set bit ND of the MR.

Thanks a lot! It works.