Running out of memory with a 30s sequence

I have two 15s stills (logo) on one track, side-by-side, that I was experimenting with. One has a colour effect and the other BCC FX Browser effect. Then there was another track above it with the same BCC effect on it across both clips. There is no audio. The effects aren'rt rendered. It's a 1080i/50 project. MC8.6.3.

I played around with it for a while and the left it overnight and memory usage was already very high: when I left it, total memory usage on my machine was ~35GB/48GB. When I came back the next morning, there was a Windows message telling me that I should shutdown Avid as I was running of memory. Closing Avid sent it (eventually) down to ~10GB after disabling the Avid Background Service Manager. When I re-started Avid and then shut it down straightaway, the total reported memory usuage on my machine was ~11.5GB, in other words, about 1.5GB went missing.

I get the impression Avid uses a hefty cache (I'm using the default cache settings) and there seems to be a memory leak when closing the application. It was only last year that I was using MC5.5. on a 16GB machine with many tracks, long sequences, and complex BCC effects with no memory issues.