GP's point (I think I agree now, I was only saying it was a potential issue) being that that's a lot easier to do at the time - you know you've just made a breaking change (or you should do; as much/more than you ever will) so that's the easiest time to bump the version appropriately.
An alternative model I suppose would immediately have major bump, minor bump, and patch bump branches; then you just commit to the appropriate one, and I suppose keep major rebased on minor rebased on patch. (And master = major I suppose.)
Right, but what if that was the second breaking change you made? To figure out whether that's the case, i.e. whether you need to bump the major version or not, you'll have to check out the last released version.
An alternative model I suppose would immediately have major bump, minor bump, and patch bump branches; then you just commit to the appropriate one, and I suppose keep major rebased on minor rebased on patch. (And master = major I suppose.)