Flexible working hours are good, right? The give you a greater degree of control over your own schedule, so you can take time off to pick up the kids, or go into the office early if you’re a morning person. By increasing autonomy and independence, they should make you happier. And chances are, if you’re a go-getter, you’ll see putting in longer hours when needed as a reasonable tradeoff for the increased flexibility.

However, it’s also becoming clearer that flexible working hours have their downsides. For one thing, flexible working hours create an expectation within families that parents will do a better job of being present; when those sometimes-inflated expectations aren’t met, workers don’t feel that they get a benefit from the policies. Some of the downsides, though, intersect with issues around gender in the workplace. In their new article “Gender Discrepancies in the Outcomes of Schedule Control on Overtime Hours and Income in Germany” (European Sociological Review, October 2016, 10.1093/esr/jcw032), Yvonne Lott and Heejung Chung compares the effects of “schedule control”— essentially the ability to set your own hours— on men’s and women’s careers, and find a disparate effect that’s worth looking at more closely.

The article’s abstract explains:

Schedule control can have both positive—e.g., increased income—and negative outcomes—e.g., increased overtime. Here our core interest is whether there are gender discrepancies in these outcomes. Given the different ways in which schedule control can be used, and perceived to be used by men and women, their outcomes are also expected to be different. This is examined using the German Socio-Economic Panel Study (SOEP) (2003–2011), and panel regression models. The results show that schedule control is associated with increases in overtime and income—but only for men. Women in full-time positions also increase their overtime hours when using schedule control; yet, they do not receive similar financial rewards. The results of this study provide evidence to show that increases in schedule control has the potential to traditionalize gender roles by increasing mainly men’s working hours, while also adding to the gender pay gap.

This isn’t the first study to observe that men and women approach flexibility differently, and are evaluated differently by their bosses. Reid and Hoffman’s study of male and female associates at a consulting company revealed that women used formal programs to reduce their working hours or go part-time, while men would politick to get onto projects that didn’t require large amounts of travel, or would just vanish from the office when they needed to do something. As a result, Reid and Hoffman found, women tended to be penalized for not being go-getters, while men who were working fewer hours but making sure they looked super-busy didn’t get penalized.

But it wasn’t just crafty workers tricking unsuspecting bosses. Reid and Hoffman found that senior partners assumed that a woman who was out of the office was doing family stuff, while a man who was out of the office was pitching to clients or at some offsite event. So while men were consciously gaming the system, they also got the benefit of the doubt.

So this kind of unexpected, unplanned gender disparity is something that companies interested in making flexible working hours or shorter working days need to be aware of. The irony is that programs that are implemented in part to make it easier for working parents and particularly mothers to stay in the workforce, and to give them an incentive to stay, can end up subtly undermining them. Designing policies that work well for everyone requires a more holistic view of work, a more intelligent approach to both overtime and time off, and an awareness of how unintended consequences can undermine good intentions.