The reason exchange-traded funds earned such tremendous traction in the market place is because they work. The ability to invest ‘real time,’ as opposed to market close, lower fees, little to no tracking error, simplicity, transparency and tax efficiency are a few of the reasons dollars flowed into ETFs.

Just for perspective, according to the Investment Company Institute, ETF assets stand at $1.2 trillion, versus mutual fund assets, which stand at about $12.3 trillion.

But I’m starting to see a small yet troubling crack in the otherwise winning façade of ETFs: actively managed ETFs. Did you ever see those jars with the peanut butter and jelly mixed together in layers? I think that’s just about the right comparison here. Seems like a logical idea–just like mixing active and passive management strategies seems logical–but in reality, not so much.

To see why this is so, let’s start by taking a look at the results of some already quasi-active ETFs. For example, investors who are seeking to invest in consumer staples could select the Vanguard Consumer Staple ETF (VDC), which is about as straight forward of an ETF you could invest in. This fund holds stalwarts such as Procter & Gamble, Coca-Cola and Philip Morris International.

Alternatively, investors could select the “enhanced” PowerShares Dynamic Food & Beverage ETF with the ironically chosen PBJ symbol. VDC has a 7% portfolio turnover rate, and a 0.19% expense ratio. Conversely, PBJ provides investors with a 134% portfolio turnover rate and a 0.63 expense ratio. Like VDC, PBJ owns Coca-Cola. Other top holdings include Monsanto, Hershey and Whole Foods.

VDC has outperformed PBJ. By a lot. For VDC the year to date and one year returns are 10.95% and 17.43%, respectively versus the PBJ’s 3.66% and 1.46%. So, that’s three times the expense for about one third of the performance.

I certainly respect the people at PowerShares, and a single comparison for a single year is hardly an exhaustive study. Moreover, I would not rule out actively managed ETFs for investors where they provide access to some specialized expertise in a far flung corner of the market.

I would say however, that for executing on the basics of most investment strategies, do what every kid over the age of five making a peanut butter and jelly sandwich already knows: don’t mix ingredients meant to be sold separately if you want a good result.