Commit 184d1550963001ad3875e11902da9d8362a93312 dropped xfce-base/libxfce4ui-4.12.1-r2 which was the last stable version available. The 4.13 series are development releases (see http://archive.xfce.org/feeds/project/libxfce4ui). While I appreciate that Gentoo lets me run current versions of software, I still prefer to run stable versions from upstream. Would it be possible to restore the 4.12 series until the 4.14 release version is available?
I don't see 4.13.0 on the page you are referring to, but 4.13.1 is not a development release. As you can see at [1], 4.13.0 is not a development release. All development relases contain the following string: "[Please note that this is a development release.]" [1]: https://git.xfce.org/xfce/libxfce4ui/commit/?id=b8cd143b87931993f8733523bf515ebd56361d42
It looks like NEWS doesn't mention whether a release a development or not, sorry for misleading: https://git.xfce.org/xfce/libxfce4ui/tree/NEWS
So it seems there is some ambiguity, which likely cannot be resolved without input from the Xfce developers. You are correct that [1] does not mention 4.13.0. On that page, 4.12.1 is explicitly called out as a bug fix release, and 4.13.2 as a development release. 4.13.1 is listed, but without any mention of its status. The Xfce release model page [2] contains the following note: Development releases usually give a feature preview for the next stable release. They must follow the X.Y.Z versioning format, where Y is an odd number (e.g. xfwm4-4.7.3 or thunar-1.3.10). From that I inferred that the whole 4.13 series for libxfce4ui is development releases, but I could have been incorrect in that assumption. [1] http://archive.xfce.org/feeds/project/libxfce4ui [2] https://xfce.org/about/releasemodel
I'm not sure if 4.13.0 should have been stabilized on Gentoo in the first place. However, it's stable for over half a year and I don't recall anyone reporting any major issue with it. So the milk is long spilled and dried, and there is no point in trying to revert that. That considered, there is really no point in you trying to force the old version (which is very old, by the way), and there is really no point in us keeping it. We are not going to support using versions older than the newest stable unless there is a very good reason to keep them. In this case, the new version has no known regressions from the old one so you can use it safely.