Element <simpletable> in DITA1.3 "concept" always lose the column widths when imported

I created a concept topic using FrameMaker DITA1.3. There is a simpletable element in this topic. I customized the column widths of this two-column simpletable to 10.1 cm and 4 cm. 

Then I saved this topic file to xml and get the simpletale element looks like this:

<simpletable relcolwidth="72* 28*" scale="100" frame="all">
<strow>
<stentry>Description</stentry>
<stentry>Remark</stentry>
</strow>
</simpletable>

But when I re-open this topic file with FrameMaker, the simpletable's columns became two equal-width columns. If I save the file in this situation, the attribute "relcolwidth" became "50* 50*":

<simpletable relcolwidth="50* 50*" scale="100" frame="all">
<strow>
<stentry>Description</stentry>
<stentry>Remark</stentry>
</strow>
</simpletable>

The read-write rules for the concept topic of DITA 1.3 is:

-----

writer use proportional widths;

...

/* Simple tables */
element "simpletable" {
is fm table element;
attribute "relcolwidth" is fm property column widths;
}

-----

If I remove the subrule "attribute "relcolwidth" is fm property column widths;", the simpletable does the same as above.

If I add another another subrule "fm property column widths value is "72* 28*"", the simpletable appears the same to above. But an message poped up in the console:

What settings override the translation of column widths based on read/write rules?

How can I customize the simpletable's column widths in the concept topic?