This seems to be specific to DECtalk 4.99 builds. Mainline versions don't have this problem. I've noticed that sometimes after a while of usage, DECtalk will stop indexing and start pausing between words. E.G. it'll start saying "this, is, a, test" instead of "this is a test." When this happens, it also stops responding to indexes. It's an odd issue and difficult to reproduce, but I think it sometimes affects the speak window in the right circumstances.