The template works by providing its own module functions which it calls instead of the mambo core ones (it doesn't overwrite the core ones, just bypasses them). With the advent of RSS feeds in 4.5.1, the module code increased in size - to include that extra code in the template therefore incurs a bit of an overhead.
If you are using RSS, then you need to call that code anyway, so the overhead is necessary, but if you don't want RSS, you might as well use the 'lighter' version which doesn't have the RSS code in it.
I wasn't aware that the menu expansion was supposed to maintain state, although it would certainly be better if it did - I'll look into that and see if I can fix it.
Cheers.