There’s a bug introduced between PHP 5.2.1 and 5.2.2 that affects
handling of Firebird blobs on 64bit machines. Having moved some of my
servers to 64bit Slackware (Slamd64 to be more precise) I run into
this problem.

Unless you want to recompile the whole PHP to a newer version with the
fix (5.3 as I understand, although did not test), you can patch the
sources: Just open ibase_blobs.c file and modify this function:

_php_ibase_quad_to_string

char *result = (char *) emalloc(BLOB_ID_LEN+1);
/* shortcut for most common case */ 
if (sizeof(ISC_QUAD) == sizeof(ISC_UINT64)) { 
  sprintf(result, "0x%0*" LL_MASK "x", 16, *(ISC_UINT64*)(void *) &qd);
} else {
  ISC_UINT64 res = ((ISC_UINT64) qd.gds_quad_high;
  sprintf(result, "0x%0*" LL_MASK "x", 16, res);
}
result[BLOB_ID_LEN] = '\0';
return result;

Rebuild the interbase.so, copy to extension directory, restart Apache and you’re done.