ace-jump slow when combined with somee vim commands

[Óscar Fuentes]

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?