NPSL are very interested in addressing bugs in gnomon. To this end, we have a public bugzilla, which is the best place to report bugs. Before you report a bug, please check to see if it has already been reported. If it has, and you want a bug to be addressed more quickly, then vote for the bug -- don't add a duplicate.

Simon Tatham's essay on reporting bugs gives an excellent overview of how to report bugs effectively. The main point is, the better the bug report, the more quickly your bug will get fixed. If possible, attach a (preferably minimal) test case.

If, for some reason, you can't make bugzilla work for you, then you can email your bug report. Please only do this as a last resort.