1.7.5 server on Linux and 1.7.5 Windows clients

When I upgraded server from 1.7.4 to 1.7.5, people playing on windows (1.7.5) clients started reporting extreme lag, and server CPU usage goes up by almost 50% of CPU per windows client connected. Other (Linux, OSX) clients do not suffer any lag, and contribute only ~10% of CPU usage per client. For the time being I reverted the server back to 1.7.4, which does not suffer from this issue.