Since a while back, there has been a branch in the public client repositories called "old". I hadn't really felt a need to announce it until now, so it is quite understandable if custom client authors haven't noticed it, but the purpose of said branch is to backport certain fixes to the pre-rendering client. The changes on that branch should be trivially mergable.
The reason I bring it up is that, as some of you may have seen, ElSid posted an experimental client with scalable UI a while ago. Since then, he packaged it up as a fairly neat patch and submitted it to me, and since this week, Jorb and I started work on trying to integrate it more properly. In doing so, there are a couple of small protocol changes that need to be made, which will be backwards incompatible with current clients. As such I've made changes to the current client (and the "old" branch) that makes it compatible with those changes, though they don't do anything else. So if you don't want your clients to start crashing, I suggest you merge these rather small and simple changes.