Can't select characters besides the first canddate

In the past couple of days and I don't quite remember when it started happening, ibus-pinyin started acting up. Right now, when I type Chinese, the first character of the character list works fine but if I wanted to choose any character other than the first candidate by pressing down arrow and then space bar on the character I want, it displays a blank space and then I am no longer able to type Chinese anymore until I switch back to English and then back to pinyin again. I am also not able to select characters by number. If I press a number, the number I press displays instead rather than the character that I choose. Has anyone experienced this? Thanks much!