There are two main ways of developing your software.
1. Incremental versions. Think like Chrome, there are not bug fixes, just new versions that may contain bug fixes.
2. Major versions, where you'll end up with semver style versioning. You'll have version 1 and version 2, but you'll also get version 1.1 released after 2 as it is the same as version 1, but with just a bugfix applied.
Debian essentially will only work with the second methodology, as they are API stable, which makes software developed by the first method incompatible.
To work around this Debian will backport "fixes" from version 3 to version 1, and create their own version 1.debian-2.
The problem here is that people will now raise bugs with upstream on behaviour that was never released.
Yes Debian is allowed to do this, but upstream is also allowed to be unhappy with the additional workload that Debian puts on them.
1. Incremental versions. Think like Chrome, there are not bug fixes, just new versions that may contain bug fixes.
2. Major versions, where you'll end up with semver style versioning. You'll have version 1 and version 2, but you'll also get version 1.1 released after 2 as it is the same as version 1, but with just a bugfix applied.
Debian essentially will only work with the second methodology, as they are API stable, which makes software developed by the first method incompatible.
To work around this Debian will backport "fixes" from version 3 to version 1, and create their own version 1.debian-2. The problem here is that people will now raise bugs with upstream on behaviour that was never released.
Yes Debian is allowed to do this, but upstream is also allowed to be unhappy with the additional workload that Debian puts on them.