Comment 14 for bug 656503

What you describe in the first paragraph is bumping the SONAME, which happens on incompatible ABI changes. Compatible ABI changes (i. e. ABI additions mostly) should only need to bump the minor version. But this patch doesn't change ABI at all.

I just saw that the package uses proper .symbols files, so it should still be possible so install the older version of the library with an application that was built against the new one, but it's still a gratuitous change which is both confusing and also unnecessary to fix this bug. You can never be too careful with libraries :-)

BTW, the numbers after the .so are unrelated to the version of the library's source package. The former track ABI changes, the latter track general development.