As quickly discussed on GitHub, there are a couple bugs which may warrant a 0.51-4 release.

In addition, here is a little list of things I think would be good fixes to have:

windows: save-to-/tmp/foo.wav bug

networking & libpd: getaddrinfo() rejects dual stack socket settings on BSD and Android (https://github.com/pure-data/pure-data/pull/1232)

mac: update patch window size after configure (https://github.com/pure-data/pure-data/pull/1236)

multi-instance & libpd: set pd_this for readsf~ and writesf~ threads (https://github.com/pure-data/pure-data/pull/1227)

writesf~: fix infinite loop on I/O error (https://github.com/pure-data/pure-data/pull/1224)

mac: add back-ported patch for Tk 8.6.10 which fixes disabled Help menu items (https://github.com/pure-data/pure-data/pull/1226), note: requires re-building and packaging Wish.app in mac/stuff