I think it depends on your income, expenses, job security, and willingness to be flexible. Also the size of the cash fund relative to annual savings, and to the purchase amount needed.
For example, if you have a 50% savings rate with wonderfully secure jobs and the cash is one year's savings, while only 1.5 years' savings is needed for the purchase, I'd invest much of it in stock index funds. Because even if stocks fall another 50%, you'd save enough in a year to make the purchase. Flexibility would be your backup plan. In other words you're safe in this scenario, why not pick up some gains?
If your savings rate is 30%, your jobs are uncertain, the cash is 2 years' savings and you need 3 years' savings to make the purchase, plus you are highly determined to buy the house at the end of this lease, I would be like the other posters and say hell no. Because your plan would fail under even a slight dip.
Stock prices are much lower than six weeks ago, but it's debatable how much better the value is. I think there's so much uncertainty and fear that the odds are now in your favor with stock purchasing, all other factors being equal - but the other factors are far more important in this case.