docbook to pdf warnings

Hi all, 

Enviroment: 
Docbook 4.5
xsltproc 
fop 0.93
cygwin 

I have a docbook document that i compiling to the pdf and have very long list of warnings that i trying to reduce/understand

WARNING: table-layout="fixed" and column-width unspecified => falling back to proportional-column-width(1)

This warning repeated countless number of time and failed to understand the reason for this warning (tables in pdf looks just as expected). 

FO output for all tables looks like the following : 

<fo:table table-layout="fixed" width="100%" border-bottom-width="0.5pt" border-bottom-style="solid" border-bottom-color="black">

          <fo:table-column column-number="1" column-width="proportional-column-width(1)"/>
          <fo:table-column column-number="2" column-width="proportional-column-width(1)"/>

          <fo:table-column column-number="3" column-width="proportional-column-width(1)"/>
          <fo:table-body>
            <fo:table-row block-progression-dimension.minimum="14pt">

              <fo:table-cell text-align="left" display-align="before" relative-align="baseline">
                <fo:block>
                  <fo:block/>
                </fo:block>

              </fo:table-cell>
              <fo:table-cell text-align="center" display-align="before" relative-align="baseline">
                <fo:block>
                  <fo:block/>

                </fo:block>
              </fo:table-cell>
              <fo:table-cell text-align="right" display-align="before" relative-align="baseline">
                <fo:block>

                  <fo:block/>
                </fo:block>
              </fo:table-cell>
            </fo:table-row>
          </fo:table-body>
        </fo:table>
      </fo:block>

I try manually change column-width="proportional-column-width(1)" to column-width="3cm" and received same error and no visual changes on pdf. 

The customization layer for may tables (only one example but they all similar) 

<xsl:template match="table_terms_and_abbr">
    <informaltable frame='none' colsep='none' rowsep='none'>
        <tgroup cols='2' align='left'>

            <colspec colnum="1" colwidth='1*'/>
            <colspec colnum="2" colwidth='1*'/>
            <xsl:apply-templates/>
        </tgroup>     

    </informaltable>
</xsl:template>

Any input on this subject will be very welcomed. As a worst case scenario i'm looking for a way to disable this warning, but i prefer fix the problem even there is no visual problem on the pdf output. 

Thanks in advance, 
Ilya.