Most likely scenario is that the size was recently changed on geocaching.com and Project-GC hasn't fetched the update yet. If the cache was edited after the most recent logs this would happen, the cache would then be fetched the next time somebody logs it.
I did a manual update of GC3EM0C and it's now an other if you add it to a virtual GPS. It will take some time before the cache is corrected everywhere and after that you're profile stats would have to re-render before you're seeing the correct number there. Doing a manual refresh of your numbers (orange support button) should probably give you correct profile stats at next rendition.
