Does it occur since last patch or was also before or you don't know?
it was even before, but I forgot to report 
Btw also no action from skillbook work in that case and so on.
In my Test from now I clicked a skill from actionbar and from skillbook after changing character.
Addons:
autodisenchant, charplan x64, combat_tools, waittimer, comeonin, waittimer, dailynotes x64, ebc, enablesystembox, extendedmacroicon, fop, functionwatch, guildpanel, lootit x64, mathe, petautoevent, petstate, raidheal, raidsm, scrutinizer, simpledamagelog, splitter, storemultibuy, titleselect, transmutor, ultimatemailmod, vactionbar, vcthreatmeter, xbar
Bugs:
parent:UI_SkillBook_SkillButton_5 call UI_SkillBook_SkillButton_5ItemButton's OnClick, line: [string "?"]:127: stack overflow
parent:MainActionBarFrame call MainActionBarFrameButton10's OnClick, line: [string "?"]:127: stack overflow
parent:UI_SkillBook_SkillButton_4 call UI_SkillBook_SkillButton_4ItemButton's OnClick, line: [string "?"]:127: stack overflow
Greetings