I'm having "cross-talk" issues with using the Solr nightlies (and probably w/ 1.3.0 release but have not tested as I needed newer features of the DataImportHandler in the nightlies)
Basic scenario for this bug is as follows
I have two cores configured and BOTH have a customized "admin-extra.html", however going to the admin pages uses the SAME admin-extra.html for all cores. the one used is whichever core is browsed first.. This looks like a caching bug where the cache is not taking into account the Core.
Basically my admin-extra.html has a link to the data importer script and a link to reload the core (which has to have the core name explicitly in the per-core admin-extra.html).