If we decide to use a piece of open sourced software that is currently released under a license that allows inclusion in an internal closed source system, what protection are we offered if the owners of the open source software decide to change the license?  Typically I'm thinking of where the new license does not allow inclusion in closed source software (I think the PDF generation api iText did this back in 2009).  Can the new license be applied retrospectively to the old versions?  I'm guessing it can, but often isn't.  We are just looking at worst case scenario, would we be in a position where we could just continue using an old version for as long as it suited and then make a decision about the future - or would we be in a position where we'd have to decide to either pay the commercial fee that is often available or find a different free alternative.
Does a License Change for OSS cover all versions, including previous releases?
open source;licensing
This question is discussed in some detail in chapter 4 of http://rosenlaw.com/oslbook.htm.The short answer is that promissory estoppel probably protects you.  But there hasn't been significant litigation on this point, and so you aren't guaranteed that this legal theory will win in court.  (And even if it was followed in the USA, you wouldn't be guaranteed that it would be followed in the UK.  Though the legal systems are close enough that they are likely to do the same thing.)If you go to a country that doesn't follow British Common Law, then the legal situation could be very different again.  I know nothing about that.