[c-nsp] C7401 problem with traffic

[Security]

Hello all

I have a strange problem with a cisco 7401. I have an Ethernet interface
connected to a BRAS for ADSL user termination. The averageoutput  traffic
of the Fast Ethernet should be around 23M. For some reason the traffic is
limited to 12M and users are compalining for slow speeds.... But I found
out that as soon as I enable IP accounting on the Ethernet interface the
output traffic increases to 23M. and the users stop complaining for slow
speeds.... I dont know why and for me it is very strange. 


IOS of c7401 is  disk0:c7400-js-mz.122-14.S12.bin wich is running fine on
other C7401 that we have. Also PXF is running on the router..

Any Idea?

Regards