Hello,
Some additional information re this bug: 
1) After submitting my report I noticed that I left a (sit-for 5) evaluation in my example.el file, which caused an unnecessary delay (it remained after debugging). I have now removed this, and the fixed example.el is attached.

2) Note that in order for all toolbar icons to appear one has to exercise the slider several times . Often moving it only once will not produce the result.
Regards,
bostjanv