First of all, thank you for getting back to me with the result of that little "update" change. It is always rewarding to know that I have been able to help.
How to not have to do the same again in the future: I have a strong suspicion that the "update" method has a bug in it, located just after the line where I suggested to "force update", but have not progressed the debugging further yet to ascertain the bug. If/when I do, I will report the bug to Photocrati.
As to reverting back to an earlier version of NextGen, I cannot say. The 2.0 version of NextGen has been a major overhaul (complete rewrite), with a switch to the MVC (Model-View-Controller) programming paradigm. Given that WordPress itself is not MVC-based, but event-based, integration was always going to be challenging at best. Whether the teething problems of 2.0 are going to last much longer, I don't know, it mainly depends on how much of an effort goes into addressing the known issues.
What does not help either is the lack of documentation/tutorials on the 2.0 NextGen architecture. NextGen 2.0 is based on a framework that was entirely developed by Photocrati, from what I understand. But there is very little in terms of developer documentation on that framework and how to use it properly, let alone on how to use it to customize NextGen (I just spent 4 heavy days trying to define of new Display Type, when in the old version, it was taking a few hours to define a new template).
Reverting to an earlier version (like 1.9.x) "might" lead to other issues: the uninstall script of 2.0 does not remove its data, and data formats are not necessarily compatible between old and new. So, if/when reverting back to an earlier NextGen version, this leftover "may" cause conflicts with the earlier version you reinstate.
There is a lot of "might" and "may": the only way to know is by trying it out (on a development site first, preferably...).