@ericwen229 sorry about the slow reply on this - I have been thinking about this.
Essentially, workflow streams and objects (and in fact Snippets) work with plain text only, so when using e.g. the Copy to Clipboard object, this is copying plain text to the clipboard (never rich text). I think you're right that {clipboard} should be evaluated to an empty string if there is no matching compatible plain text string. I'll get this sorted in the next release
