The rise of flexible work arrangements comes with one risky drawback.

When working nontraditional hours (evenings or weekends, for instance), employees experience a decrease in their sense of intrinsic motivation, which in turn decreases their productivity and happiness, according to a new study from Harvard Business Review. Although previous research from the International Workplace Group shows that 80 percent of workers prefer employers that offer flexible work, HBR's latest findings--gathered from a survey of 2,000 employees and students--shows that flexible work, in practice, has surprising challenges.

There are certainly benefits to flexible work arrangements. Giving employees more control of their schedules can help them be more productive when they have fewer distractions like meetings and notifications. Flexible hours can also make it easier for working parents to find work-life balance.  

The downside? It can eventually lead to feelings of burnout, as employees begin to feel negatively about toiling during times that might traditionally be used for leisure, the authors of the HBR study, Laura M. Giurge and Kaitlin Woolley, note.

The solution is to encourage a mindset shift. When leaders remind team members of the benefits of their flexible work hours, they feel less negatively about working untraditional hours. Prompts like calendar reminders or timer apps, which can better distinguish when it's time to work, can also help employees execute the shift into flexible work without making them feel like they're sacrificing something. The point of flexible work hours is to give workers the option to set their own schedules--not to lengthen the workday or to take over relaxation time. Helping employees better separate their work from their leisure time, especially during nontraditional hours, can help them stay motivated and happy.