Annoying memory problem

I am running 8.5 producer on windows xp 64 bit. For some odd reason on some of my projects, every time I hit the play button, it wants to use more and more of my RAM until it is using so much of it that I have to restart the program and reopen the project at which point the memory usage has magically dissapeared. As I say this only happens on certain projects, with other projects, despite using exactly the same type and number of plugins, being fine to play as many times as I want. Anyone know what the problem is?

Right ok. Seems rather annoying. Oh well I've frozen the tracks with delay on anyway so I'll just have to save the settings and load it back up again if I need it. Thanks!