MarketPress requiring an absurd amount of memory

Some information:

Memory use
total used free shared buffers cached
Mem: 995 406 589 0 24 168
-/+ buffers/cache: 212 782
Swap: 2998 0 2998

As you can see, I have over 500MB of free RAM in addition to swap space.

My relevant PHP settings for this site are as follows

memory_limit=528M
max_execution_time=240

Any attempt to visit the administration page results in the following error:

Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to allocate 292606 bytes) in /home/paper/public_html/wp-includes/functions.php on line 251

Is this usual behavour? It’s upsetting that I can’t even use marketpress on a VPS, let alone bothering to try and use it on my clients shared hosting.