shareInstances are resolving but don't always propagate

[lkrms]

While writing tests for a project that's adopting Dice, I stumbled on an edge case where shareInstances appear not to resolve because multiple instances of the relevant classes are created by Dice->create().

(It turns out they do resolve, but are subsequently removed by matchParam().)

I've added the edge case to ShareInstancesTest to make it easy for others to replicate, and have prepared a patch in keeping with the minimalist philosophy that brought me here in the first place, but I wasn't sure if issues were preferred for tagging and documentation purposes. So, I'm reporting this as an issue and will now go and open a PR ;)