Not really. The build size itself should be less than 300k anyway, which means a 100k increase would be very very significant. Then there's the fact that you're running Rockbox from flash, right? Which means that what's using space are the various other buffers for fonts, plugins, etc, rather than an actual increase in size of Rockbox. It would be really strange for someone to have allocated 5% of the Archos' RAM for something in the last month.
Have you cleared your settings, and then shut down and started back up, to see if that affects the amount you have available?