@tazzydemon I think your experience can be explained by the following open issue:
Which you commented on in Feburary.
Unfortunately the timing of CentOS 1611 release for the last iso remaster was just a little too close, please see @suman comments in that issue on this. However once installed a Rockstor system will then update to the latest 1611 release.
That would appear to explain the installer discrepancy.
If you take a look at the rockstor-iso repo you may very well be able to master your own iso using the 1611 variant from upstream and any feedback on your experience doing that would be really handy for when the time comes to remaster the next Rockstor ISO.
Do feel free to add comments to that issue so that we might gather related info on this.
Either that or we have a bug in how the latest iso is constructed (most likely relating to UEFI install I would guess). Please do review the script and ks.cfg file used in that repo.
I have linked back to this forum thread from the above issue in an attempt to tie such reports together.
Hope that helps to explain the discrepancy, ie our installer is based on 1511 but the first update takes things to 1611.
Also linking here to a former forum post of yours re UEFI install failing on Braswell N3700 UEFI which is already linked in the above issue.