Custom date format won't save correctly

When trying to apply a custom date format of any kind to my site, it results in the following:

2012-06-16T15:55:29+00:000000002930201206

All of the provided date formats work, but if the custom field is selected, nothing works.

I would like to use a simple M d format to result in a Jun 16 output, but nothing works.

Any suggestions?