FOP rejects a property value of "inherit" as an unknown value for the following
inheritable properties:

font-weight  font-style   position   hyphenate   white-space-collapse   
wrap-option  text-align   text-align-last  

For the font properties, FOP simple passes the string "inherit" causing an error 
unknown font sans-serif,italic,inherit

Code:

<?xml version="1.0" encoding="ISO-8859-1"?>
<fo:root xmlns:fo="http://www.w3.org/1999/XSL/Format" xmlns:src="UBSXMLSrc">
<fo:layout-master-set>
<fo:simple-page-master master-name="seiten" page-height="29.7cm"
page-width="21cm" margin-top="2cm" margin-bottom="2cm" margin-left="1.8cm"
margin-right="2.0cm">
<fo:region-body column-count="3" column-gap="2mm" margin-top="1.0cm"
margin-bottom="2.0cm" />
<fo:region-before region-name="s2ff-before" extent="2.0cm" />
<fo:region-after region-name="s2ff-after" extent="2.0cm" />
</fo:simple-page-master>
</fo:layout-master-set>
<fo:page-sequence master-reference="seiten" initial-page-number="1">
<fo:static-content flow-name="s2ff-after">
<fo:block font-size="11pt" font-family="sans-serif" line-height="13pt"
text-align="center" padding-top="12mm">
<fo:page-number />/<fo:page-number-citation ref-id="IDAWEF4" />
</fo:block>
</fo:static-content>
<fo:flow flow-name="xsl-region-body" font-weight="bold" font-style="italic"
position="relative" break-after="page" hyphenate="false"
white-space-collapse="true" wrap-option="wrap" span="all" border-style="solid"
border-color="red" border-width="1px" text-align="end" text-align-last="start">

<fo:block span="all">
This flow has the following properties. These properties should be inherited by
all blocks on this page that do not specifically override the settings
 font-weight="bold" font-style="italic" position="relative" break-after="page"
hyphenate="false" white-space-collapse="true" wrap-option="wrap" span="all"
border-style="solid" border-color="red" border-width="1px" text-align="start"
text-align-last="end"
</fo:block>
<fo:block font-weight="inherit">Block with font-weight of ="inherit"</fo:block>
<fo:block font-style="inherit">Block with font-style of ="inherit"</fo:block>
<fo:block position="inherit">Block with position of ="inherit"</fo:block>
<fo:block break-before="inherit">Block with break-before of ="inherit"</fo:block>
<fo:block hyphenate="inherit">Block with hyphenate of ="inherit"</fo:block>
<fo:block white-space-collapse="inherit">Block with white-space-collapse of
="inherit"</fo:block>
<fo:block wrap-option="inherit">Block with wrap-option of ="inherit"</fo:block>
<fo:block span="inherit">Block with span of ="inherit"</fo:block>
<fo:block border-style="inherit" border-color="inherit"
border-width="inherit">Block with border-style of ="inherit" border-color of
="inherit" border-width of ="inherit"</fo:block>
<fo:block text-align="inherit">Block with text-align of ="inherit"</fo:block>
<fo:block text-align-last="inherit">Block with text-align-last of
="inherit"</fo:block>
</fo:flow>
</fo:page-sequence>
</fo:root>