Well mine also has that same problem. SED increases memory usage everytime I run my scripts but somehow it depends on the memory used by the scripts.
For example, each time I run my dinoisland, the memory usage increase about 30Mb, while some example almost no significant increment. The solusion is just simple, I quit SED then restart it again... Maybe some kind of memory leak...

Well since I use LLiteC Free which is free, I have no complain though...