Comment 4 for bug 1424602

It's standard in Debian and Ubuntu to provide the .so symlink only in the -dev package. This is because anything linking against it at runtime should access the version of the library it has specifically been built with (or designed for) by accessing <libary>.so.<version>. Otherwise it could pick up the wrong file and this would break things.

On the other hand, when developing you generally want to link against the "current" or "latest", so the symlink is provided for that (but you shouldn't install the -dev packages from multiple versions at once).

As this is the standard for all packages in Debian, we can't treat it as a bug unless there's some specific reason that this package should diverge from the standard.