BUG: named time references problem in formula

[Daniele Pizzolli <dan@toel.it>]

Hello,

according to [[info:org#References]] (see Named references) is possible
to use a property in formulas. This generally works, but not when the
property is a time value as defined in
[[info:org#Durations%20and%20time%20values]].

Please have a look at the following ECM:

* test table with constant (working)
   :PROPERTIES:
   :constant: 3
   :END:

| month |  days | results |
|-------+-------+---------|
|    01 |     1 |       3 |
|    02 |     3 |       9 |
#+TBLFM: $3=$2*$PROP_constant;


* test table with time constant (not working)
   :PROPERTIES:
   :time_constant: 08:00:00
   :END:

| month | days | time |
|-------+------+------|
|    01 |    1 |      |
|    02 |    3 |      |
#+TBLFM: $3=$2*$PROP_time_constant;T

Pressing C-u C-c C-c over the table shows in the message buffer:

org-table-eval-formula: Wrong type argument: stringp, (13 "Bad format")

Also is not possible to debug the code even with the formula debug
enabled.

Omitting the ";T" part will cause the debug to work and then the string
#ERROR show up in the cell.

My version is Org-mode version 8.3beta (release_8.3beta-1080-g367d48 @
/home/user/.emacs.d/el-get/org-mode/lisp/)

Best,
Daniele