Hello,

>
> From Vim's help (":he ft"):
>
> When a dot appears in the value then this separates two filetype
> names. Example:
>
> /* vim: set filetype=c.doxygen : */ ~
>
> This will use the "c" filetype first, then the "doxygen" filetype.  This
> works both for filetype plugins and for syntax files. More than one dot may
> appear.
>
> Unfortunately, taglist doesn't support dotted filetypes. For instance, I open
> a C++ file and set the filetype to "c.cpp". This shouldn't affect the
> behavior of taglist, but when I :TlistOpen, I don't see anything. With a
> filetype of cpp or c alone, it works just fine.
>
> Is this know/expected behavior?
>

The taglist plugin currently doesn't support dotted filetypes.
I will add this to the todo list.

- Yegappan