See this.
@antonis: First of all, it makes no sense to report this. Squeekboard has newer versions (that do not run on Byzantium by default) and even if there is a bugged version, I’m mostly sure the current one is free of such bugs. You could try out to install a custom layout. For example the official up-to-date version. Copy it into home/.local/share/squeekboard/keyboards/ and try if this fix your issue.
A backport of the newest version would be another possible solution. Maybe someone else also has another idea.