If you look at the command line, it contains this flag -Xmx256M which means reserve 256M. Until the 256Mb level is reached the heap will continue to grow.
The same thing happened to my buddy in TWS. Too bad he did'nt know what was going on because it was spyware or hacker code that he mistakenly or unknowingly downloaded and they ended up cleaning out his account.
It took them three days to do it and that's why for three days his memory usage was going up all the time--the hacker(s) were trying to figure out how to rip him off.