String parameter is ignored if numeric, why?

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I am requesting a string parameter from the parameter server in ROS Groovy like this:

ros::NodeHandle node_ns("~");
std::string rotations;
node_ns.param<std::string>("rotations", rotations, std::string("0"));

When I run my ROS node with the following command line, everything works fine:

./bin/testnode _rotations:='90 -90 0'

i.e. if I check the value of the string "rotations", it is "90 -90 0". However, if I only input a single numeric value as the string's value,

./bin/testnode _rotations:='270'

the supplied value is ignored and "rotations" has its default value of "0". I think this occurs because the single value is treated as an integer instead of a string. Is this a bug? This can have pretty nasty consequences! I was debugging my code for over an hour trying to figure out why my supplied parameter value was being ignored although it had worked perfectly in other cases...