Failure to set item check interval to anything larger than 1d

When configuring an existing item to have an update interval of n days with n >1 using the string '2d' (for example), the update fails with the error: "Item will not be refreshed. Please enter a correct update interval."

This happens when reconfiguring the item using the webinterface, but also when reconfiguring the item using the api.

I would have expected the error message to either give details as to what was incorrect about the interval (since the time modifier 'd' is supported according to the docs), or Zabbix to not give an error at all and update the item to the desired interval.