This is similar to an issue discussed
http://www.openoffice.org/servlets/ReadMsg?list=users&msgNo=85855

When several lines are selected, in which there are different tabs set for
different lines, there are no tabs shown on the ruler (and the list of tab stops
in the format paragraph dialogue is empty). 

For example, this issue occurs for a table (entered as text and arranged into
columns using tab stops; effectively a tab delimited text table; not an Ooo
Writer table), and the first line(s) of the table, which contains titles of the
columns, has different tabs to rest of the table (a decimal tab is useful for
numerical columns in the table, but will offset the column's text title, so a
left or right tab is used to arrange the title for that column). 

When the rows of the table are selected, so that the entire selection has
consistent setting of tabs, these tabs are displayed on the ruler, and in the
table of tabs in the Format Paragraph window. 

If a line with a different tab setting is ALSO selected, then no tabs are
displayed. 

Perhaps this could be handled more elegantly. We use these text-tables because
it is inherently simple to move the contained data into and out of spreadsheets,
and from other applications. Also, these tables export conveniently to ascii
text files. 
The writer tables, at this point, do not allow us to move such large volumes of
data into and out of the document while still retaining such simple text structure. 

I set the Priority to P5, as it is only a very minor annoyance, and it only
happens when handling inconsistently tabbed lines.
It is of particular annoyance where there are many tabs set in a large table
(hundreds of lines, with up to 12 columns), and the tab of one line of data has
inadvertently been adjusted or removed (or a line has been inserted which had
different tab settings and they have been retained). So when the selection is
made, no tabs are displayed. I either locate the offending line (not always
obvious) and change it to conform (ie cutting and pasting without formatting to
capture the tab settings of the preceding line), or I force the entire table to
conform by cutting and pasting without formatting to capture the tab settings of
the first data line.