My first test build (1.5.29-333.1) didn't solve the problem for me. I found another ibus upstream commit which fixes an issue which looks even more like the problem I'm seeing: https://github.com/ibus/ibus/issues/2588 https://github.com/ibus/ibus/commit/4872c1fcdc8bbe146e967d004edf63f5994b21f8 So I backported that commit as well, and the new build (1.5.29-334.1) fixes my problem. I hope it will fix Michael's problem too.