utf8_encode and iconv

I am trying to convert an iso-8859-1 string with accented characters to
utf-8.
For instance, here is one : à7ç1ç6êñt

On windows machine with php 5.2.5  , both functions succeed .
On Gentoo php 5.2.6 , the character à gets lost and anything the '7' is
preserve including the accented characters.
This is true for any accented characters preceding a non-accented character.
If these accented characters precede
a non-accented character , these will get lost.

Has anyone seen this before ?