OK, I can repro the issue. What's happening is that on the 4th step (Add Now), on the default database with test products, I get correct attributes and options:
<input type='submit' value='Add now'><input type="hidden" name="id[3][value]" value="8"><input type="hidden" name="id[3][type]" value="0">
but on my database, these fields have been damaged:
<input type='submit' value='Add now'><input type="hidden" name="id[26]" value="Array"><input type="hidden" name="id[27]" value="Array">
(which creates empty values in orders_products_attributes.
So going back a step, on the default database in step 3, I get
<label class="attribsSelect" for="attrib-3">Model</label><select rel="dropdown" name="id[3][value]" id="attrib-3">
and on my database, I get
<label class="attribsSelect" for="attrib-27">Mounting Orientation:</label><select rel="dropdown" name="id[27][value]" id="attrib-27">
which looks the same to me.
Gets into init_sanitize fine, but goes from ./includes/classes/AdminRequestSanitizer.php into filterSimpleAlphanumPlus which clobbers the array (line 335).
It looks like on my side, the ParameterDefinitions array does not include the entry for MULTI_DIMENSIONAL.