Hello again,
said issue is merged (https://issues.guix.gnu.org/63327) now.
Unfortunately, it does not affect openjdk10, since it uses a different file system organisation than the former version.
I already suggested this solution to bug#63069 (https://issues.guix.gnu.org/63069) where a fix along the lines of separate patch files was proposed as a better alternative to issue #63327.
Still keeping this open until a patch for openjdk10 has been merged, too, which I would love to see soon.
Cheers
Tim