If you are relying on unpaid open source code for commercial work, you should fully understand what that means for you:
> This software is provided 'as-is', without any express or implied warranty. In no event will the authors be held liable for any damages arising from the use of this software.
(from the zlib license, but others have similar disclaimers)
If that is a problem for you, negotiate a different contract up front - with the maintainer or someone else willing to do the work. That probably means paying them.
If you don't then no, the maintainer is not required to invest the time and money you are unwilling to into maintaining your pet feature or "fix".
> This software is provided 'as-is', without any express or implied warranty. In no event will the authors be held liable for any damages arising from the use of this software.
(from the zlib license, but others have similar disclaimers)
If that is a problem for you, negotiate a different contract up front - with the maintainer or someone else willing to do the work. That probably means paying them.
If you don't then no, the maintainer is not required to invest the time and money you are unwilling to into maintaining your pet feature or "fix".