ace-jump slow when combined with somee vim commands

When I execute M-x evil-ace-jump-char-mode [CHAR] it instantaneously highlights the candidates. However, if I do (in normal mode) d M-x evil-ace-jump-char-mode [CHAR] it is very slow. On a netbook I can see how each candidate is highlighted individually, taking approx. two seconds when there are about 20 candidates. The slowdown is observable on a workstation-class machine too, but not as evident/annoying. What can cause this? Any ideas for investigating the problem?