YahooFinanceSource Caching is a bit opaque

[meltyness]

I didn't see this anywhere in the docs, but if the cache pulls a miss, it caches the miss somewhere. To anyone else seeing something like "data not available" on subsequent runs:

bt.prices.clear_cache()

Should fix it right up.

[MiniXC]

I've encountered this before as well. I will have a look, this shouldn't be too hard to fix.