Attached spreadsheet has 2 colums: Street and No.
If used as datasource, the street numbers with letters in them aren't displayed.
If MailMerge is done, the affected data are not merged (thus they are lost in
output or print). The behaviour probably cannot be affected by regular actions
of ordinary user, if it can be affected either.

I've formatted all cells as Text, and then the Column Format was set to Text too
in data view. (F4 key in word processor)

The database layer should
1. Either verify the real data type from each cell's format settings
2. Or allow user to set them manually
3. Both:
First step -try to guess the type by scanning the cells for each column.
Second step -allow user to change it, with DB Source View open so that he can
see, what he get

Notes
1. Don't know if it affects all databases or just Calc spreadsheets source
2. May be related to
http://www.openoffice.org/issues/show_bug.cgi?id=24671
http://www.openoffice.org/issues/show_bug.cgi?id=4122
http://www.openoffice.org/issues/show_bug.cgi?id=31472
http://www.openoffice.org/issues/show_bug.cgi?id=34992

3. Although for me it seems like bug and for sure it leads to unexpected loss of
data (P2), the developer 'clu' insists that this is an enhancement. So I'm
reporting this as enhancement.