This is one is a little bit complicated. Here's some background information on it:
Upstream BusyBox handles shell history perfectly well. Even Maemo's stock BusyBox handled shell history well, until bug 4174 appeared, that is. As you can read there, it changes BusyBox' shell history saving behaviour from writing out the history directly after executing a command, to saving the history upon shell exit. This, however, introduces new problems (e.g. bug 5317 you've mentioned).

It's a tradeoff we have to make here. Either we keep the proper upstream shell history handling and have a (little?) bit more wear on the eMMC and a resulting (small?) increase of power usage, or we go Nokia's way of saving shell history only upon shell exit, but then we'll have problems with concurrent shells etcetera.

Apparantly, Nokia has left out their shell history patch in Harmatten, thus the bug you've mentioned is 'fixed' for Harmatten. Bug 4174, however, is reintroduced there AFAIK.

I'd like to stick with what Nokia has decided to do for Maemo 5 in the first place, which is including the shell history patch. Some averaged numbers (/guesses) on how much wear upstream shell history handling actually creates on our eMMC's would be great, but I guess those are pretty hard to quantify.

However, to give you the freedom to choose yourself, I've compiled the latest busybox-power without shell-hist.patch; click here to find it. That build should suit your shell history needs . I'll keep this alternative busybox-power version up-to-date, but I currently don't have any plans to push it to the repositories.
Update: Scrap the previous line. Since busybox-power 1.18.5power3, shell-hist.patch has been dropped in favor of a new patch. This new patch fixes all mentioned problems, so there's no need to maintain the special busybox-power build. I can, however, create a new version of it without the new patch if there's any demand for it (drop me a PM).

Patching the code won't do, unfortunately. It's either saving the history at exit, or saving it after each line; both with their own pros and cons. That, or we need some code to keep the history from multiple terminal instances in memory somehow, and write it out when the last terminal instance closes. However, that's a bit out of my league I'm afraid

Anyhow, thanks for the workaround, I seem to have missed it in the bugreport itself earlier. I'll certainly include it in the next busybox-power release.

Already fixed :