In D6272#145234, @Philipp Oeser (lichtwerk) wrote:

dont want to hijack, but reminds me of D1578: fix Custom Python Nodes dont draw their 'bl_icon'

Thank you for pointing this out – I've updated the sample script to reflect this. The issue still remains as described.

Operators like this should not change the active object automatically, as pointed out by Brecht Van Lommel. Instead, the operator checks for active object (if active object is None, mode cannot be 'edit')