Not much to go on here, none of any log produced by the server or client give details on what, where or why.

Mojang's “Minecraft game output “console window” constantly throws this, which the output marks as an error:

-Unavailable URL-

After running the latest build #93 for several hours I've determined the memory leak is happening with these objects -Unavailable URL-

the green bar representing there memory usage when i took a snapshot of the memory, red bar being increase in memory over time

Normal behavior would show an increase, but then a decrease to normal (or lower) on regular intervals it does not appear these objects ever decrease the amount of memory they use.