Any changes made to a current release are generally published in the next release.
There is no reason not to have maintenance branches (particularly if started at the behest of users taking commercial support - though of course these branches would be open source and published on GitHub), but where it makes sense, we tend to favour just putting changes in the trunk.
This is especially so for enhancements as opposed to bugs (and regressions in particular). I view the table row height change as an enhancement.
As I just wrote in another thread:
2.8.1 was released quite recently. Ordinarily, we'd make more improvements before rolling another release. However, given the issue with nested tables in PDF/HTML output in 2.8.1, a next release could be sooner rather than later. There's
https://github.com/plutext/docx4j/issues/13 which needs to be in the next release. So, it would be good to release 2.8.2 in November.
The issue with nested tables in PDF/HTML output in 2.8.1 is a good example of a fix which is a candidate for a 2.8.1 maintenance branch. But if we do publish 2.8.2 so soon, I see no reason to also have a 2.8.1.1. Comments welcome.