Not really a bug right now, but could be in the future. In the 2016.14 version of xlights with the new drag and drop for the models, the custom models don't show anything in the layout when you put them there. This means you can't see if you have selected the model or not to move around, or more importantly delete. The only way to delete that is to bring up the model list window and delete it... the CRTL-X doesn't seem to work. In the meeting last night Dan said he wanted to get rid of that window in the future. If that happens, not sure there would be a way to get rid of a custom model without first putting something in it, then selecting it and deleting it.
Loving the new way of making models! Thanks for all the great work.