The following codes:

X509Certificate cert= (X509Certificate) cf.generateCertificate(new FileInputStream("cert.in"));
FileOutputStream certOut= new FileOutputStream("cert.out");
certOut.write(cert.toString().getBytes());
certOut.close();

The cert.out contains the following IOException:

Unparseable certificate extensions: 1
[1]: ObjectId: 2.5.29.17 Criticality=false
Unparseable SubjectAlternativeName extension due to
java.io.IOException: Invalid encoding of RFC822 name

0000: 30 34 A1 1A 16 18 65 73 63 65 72 74 2D 75 70 63 04....escert-upc
0010: 40 65 73 63 65 72 74 2E 75 70 63 2E 65 73 A6 16 @escert.upc.es..
0020: 16 14 68 74 74 70 3A 2F 2F 65 73 63 65 72 74 2E ..http://escert.
0030: 75 70 63 2E 65 73 upc.es
0000: 30 34 A1 1A 16 18 65 73 63 65 72 74 2D 75 70 63 04....escert-upc
0010: 40 65 73 63 65 72 74 2E 75 70 63 2E 65 73 A6 16 @escert.upc.es..
0020: 16 14 68 74 74 70 3A 2F 2F 65 73 63 65 72 74 2E ..http://escert.
0030: 75 70 63 2E 65 73 upc.es

While one other solaris 10 x86 it generates the following:

Unparseable certificate extensions: 1
[1]: ObjectId: 2.5.29.17 Criticality=false
0000: 30 34 A1 1A 16 18 65 73 63 65 72 74 2D 75 70 63 04....escert-upc
0010: 40 65 73 63 65 72 74 2E 75 70 63 2E 65 73 A6 16 @escert.upc.es..
0020: 16 14 68 74 74 70 3A 2F 2F 65 73 63 65 72 74 2E ..http://escert.
0030: 75 70 63 2E 65 73 upc.es

These toString encodings at least don't conform to each other. They should be conformative.
This only happens on some particular cert files. The following two cert files are of these types.
/net/sqesvr-nfs/global/nfs/sec/ws_6.0_int/security/src/X509V3/interop/badCerts/certv3.crt.data
/net/sqesvr-nfs/global/nfs/sec/ws_6.0_int/security/src/X509V3/interop/badCerts/myset.crt.data