Disclaimers: it is not 1.5GB file, just 700K (biggest in my N900 right now) and I am running root FS on /home partition + swap in uSD. But I feel it should be not a reason for such big difference. We can look somethere else... Actually, I had this problem (freeze after big file copying) but it was on PR1.0 6 month ago. I thought it was fixed...