Is is a limitation of the plugin or a bug ?
Oh, my god! This is million dollars question! The answer is depend on your philosophy.
In general case, when user want to copy file from FS-plugin there exists two possibilities:
1. Old good FS-plugins. File in such plugin is not real file (like single mail in mail plugin or event in Calendar plugin). In this case, obvious, no one except plugin itself could copy such file.
2. "Virtual Panel" plugins introduced in TC7. File in such plugin represents a real file on disk. Who should copy this file. Should it be done by plugin or by TC? I'm sure - by TC. I'm definitely not going to write copy procedure comparable with TC power (comments, overwrite dialog, BTM, etc, etc, etc). So from my point of view it is not bug but leak in TC.