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Strangeness when binary executable overwritten by text -- bug or feature?

Debian 9.1 with MATE installed from DVD set.

Due a non-reproducible sequence of events, a binary executable was over written by the contents of a man page in pure text format. For unknown reason, the resulting file was tagged as executable.

A custom MATE launcher pointed the corrupted file.
When the launcher icon was clicked there was no response whatsoever.
Is this a bug or a feature?
If a feature, why?