12c datapatch can fail with manual out of place patching

datapatch can fail if doing manual out of place patching, when the new ORACLE_HOME is not cloned from previous one but a fresh installation. The problem is a one-of patch in the old ORACLE_HOME, which is included in something else (like a PSU) in the new ORACLE_HOME.
In my specific situation the old O_H had PSU 12.1.0.2.3 + some one-off + Patch:21355879.
This Patch is not needed anymore in my new O_H (12.1.0.2.4 + some other one-off) - I checked on My Oracle Support - Patches & Updates:

So no need (and no simple way) to add this patch to the new O_H at all.

But when running datapatch within the new O_H, it throws this error and refuses to continue:

Error: prereq checks failed!
  patch 21355879: rollback script /appl/oracle/product/rdbms_121024Jc/sqlpatch/21355879/19095143/21355879_rollback.sql does not exist
Prereq check failed, exiting without installing any patches.

It's obvious the patch  21355879 is not installed within the new O_H. But somehow ( I did not check the exact internal function) datapatch checks the view DBA_REGISTRY_SQLPATCH and finds PATCH_ID:21355879. With a statement similar to

SELECT XMLSerialize(CONTENT dbms_sqlpatch.opatch_registry_state INDENT) from dual;

it finds the patchuid 19095143. The base table seems to be OPATCH_XINV_TAB.  (the other patches within 21355879 are not in this XML and doesn't require a rollback script).

So the database repository says a rollback script should be present, but it's not installed in the new O_H as Oracle calls it not required anymore.

The clean solution would be to patch every new O_H in the exact sequence of all it predecessors - this can be time consuming and also challenging when different branches with conflicting one-offs needs to be merged - even all these conflicting one-offs are merged in a later PSU and not needed anymore.

We decided to do the easier way and just copy all patch directories from old onto new O_H.