Module still unbound even after cmo has benn #load-ed

This morning I copied my "root" OCaml directory containing all
my OCaml projects, to a different location on the same computer.
But a lot of weird things happened when I started to work in
the new directory. 

In case someone should ask, yes I checked that my makefile does
not contain any mention of the path to the directory it's in, and
yes when in my new directory first thing I did was delete all the cma/o/i's and
recompile everything from scratch (and I repeated this operation when
trying to figure out what was wrong).

The weird things happen with my customized toplevel :

Weird phenomenon 1: even though the production/compilation
of the toplevel goes fine with zero warnings, the created
toplevel only knows about the modules whose .ml file is
situated in the root dicrectory. All the modules whose .ml
file is situated in a subdirectory are declared unbound.

Weird phenomenon 2 : When I see that my toplevel does not 
know about the module implemented in subdir/my_module.ml,
I naturally try the directive #load"subdir/my_module.cmo".
The toplevel recognizes the file (I know that because it does
not issue a "Cannot find file" message), but the module
My_module is still unbound after the directive has been
executed.

Any help appreciated.