Hi,

f90-mode sets by default indent-tabs-mode to nil, which is good for me.

If I want to set automatically (indent-tabs-mode t) for the rest of the
modes, I set .dir-locals.el to

--8<---------------cut here---------------start------------->8---
((nil (indent-tabs-mode . t)))
--8<---------------cut here---------------end--------------->8---

However, that sets the variable to nil even in f90-mode, as expected.
The problem is that I cannot revert that setting for f90-mode even being
specific in .dir-locals.el:

--8<---------------cut here---------------start------------->8---
((nil (indent-tabs-mode . t))
 (f90-mode . ((indent-tabs-mode . nil)))) ; It is evaluated to t nevertheless
--8<---------------cut here---------------end--------------->8---

This is somewhat strange, according to the manual.  Are there any
pointers for further debugging this issue?

Thanks!

-- 
Alberto