Environment variable initialized with setenv are not correctly appended later in modulefile

[xdelaruelle]

Describe the bug

When defining an environment variable with setenv in a modulefile, if this variable value is later in the modulefile appended (with append Tcl command), initial value set with setenv has disappeared.

To Reproduce

Steps to reproduce the behavior:

With the following mod modulefile:

$ cat mod
#%Module
setenv FOO foo
setenv BAR $env(FOO)
append env(BAR) bar

Load this modulefile then check value of BAR variable:

$ ml -v ./mod
Loading /path/to/mod
$ echo $BAR
bar

Expected behavior

Resulting BAR environment variable should equal to foobar not bar, as it is first initialized with foo value.