Fortify Attribute effects do not stack when Spellmaking.
In vanilla MW you can stack the various Fortify Attribute effects so that one spell can fortify both INT and LUCK, for example, as in attached image. In OpenMW when you try to add the second effect you get a "This effect has already been added" message. I suspect attempting to add more than one fortify skill effect would have the same result, but haven't been able to test it yet.
(RM-2224 from redmine: created on 2014-12-21 by Carl Daugherty, , closed on 2014-12-26 by Miroslav Remák)
Edited by redmine