[willis77]

Some bikes that are hard to ride no-handed have "notched"/"indexed" headsets that are to blame. Small indentations in the headset prevent minor corrections from actually turning the wheel, making it hard to let go of the bars.

http://www.sheldonbrown.com/headsets.html#troubleshooting

(see section on "Indexed Steering")

[etcet]

Thank you so much. My bike has been exhibiting this behavior but I just assumed the headset was designed to 'clip' into place. Looks like I need to see the mechanic.