Any expression enclosed in parentheses always results in only one value. Thus, (f(x,y,z)) is always a single value, even if f returns several values. (The value of (f(x,y,z)) is the first value returned by f or nil if f does not return any values.)
You have to notice that the parentheses for the function call and those extra ones are two different kinds.
I'd guess that this is caused by the addons themselves. Their zip files seem to include these folders on top level but they are likely not set up as dependencies. So the addons are more like multiple addon packs with conflicting files.
So these conflicting files aren't handled via the client's lib/no-lib system but by the generic archive (un-)install.
Just had a quick look at the AceGUI code itself (something you could have done yourself ;) ).
AceGUI:Create(type) returns an AceGUI widget of the given type and while there is a "frame" type, this isn't a normal frame. It thus doesn't have the same API.
In theory, you could dig into its internal frame and set the options there but these wouldn't be cleaned up on release.
So the best way would likely be to clone your own custom widget from the frame widget.