Proprietary software is software that has bugs that can only be fixed by the company owning the source code to the software.
Proprietary software is generally written by a limited number of humans and therefore has the same potential for errors and bugs as any other software, but a smaller potential for getting the bugs fixed than free software.
Proprietary software is in many cases about increasing the freedom for the manufacturer to make a product without the major concern being quality and decreasing the freedom for the customer for copying, sharing and changing the software to their own ends.
Proprietary software lets users believe they have purchased something akin to a physical object, although software is nothing of the kind.
Proprietary software companies often has a help line that the customer can call when their software doesn't work as they expect or as advertised. But no phone call to a help line operator that knows nothing about programming can ever fix a bug in the software by itself.