I think there is a common misunderstanding of the meaning of the word “stable”.
The word “stable” has many definitions, but the two that are relevant here are:
- Unlikely to fail
- Unlikely to change
When we talk about software, “stable” generally means that it is unlikely to crash or have problems (definition 1). But when we talk about a Linux distribution and/or its various channels, the word “stable” generally refers to how often it changes (definition 2).
This may make more sense for a distribution like Debian: once released, the versions of software available in the Debian repositories do not change. This is why in the current (as of 2024-08-25) version of Debian 12, KDE Plasma is still at version 5.27.5 (Manjaro is at 6.0.5), and Gnome is at version 43.9 (Manjaro is at 46.4). Naturally, Debian’s stable (def. 2) channel’s software will tend to be more stable (def. 1), because they will receive only backported bug and security fixes over their supported lifetimes; but that stability (def. 1) is just a side effect.
The name “stable” makes a little less sense in the context of a rolling-release distribution like Manjaro. But in the context of Manjaro’s channels, we can clearly see the difference in the relative rate of change between “unstable” (changes every few hours) and “stable” (changes every few weeks). There is no guarantee that stable (def. 2) channel software will be bug-free; the only guarantee is that such software will not change as frequently.
Therefore, there is nothing inherently contradictory about a stable (def. 2) channel containing unstable (def. 1) software. Or an unstable (def. 2) channel containing stable (def. 1) software, for that matter.