I know that Ashley has said that Construct is developed on Win 8 (correct me if I'm wrong.. this is something I read ages ago...) so that always nulls the "Oh cos of win 8" argument.
I doubt Scirra's business plan is "crash every so often to force people to buy our product" either! So likely not because of the free version.
My construct only crashes when I 'undo' about an hour's worth of work (because I realise it just doesn't work) and then it starts getting laggy and then just crashes.
Other than the above, it doesn't crash on me:
Using Dell Laptop with i3, built in intel 4000 graphics (so nothing special.)
By the way... are you using dropbox or weird folders as backups? I've had this thing before where if it is set to somewhere it doesn't exist it just goes mental..
Otherwise no idea, sorry :-)