I'm pretty sure most instances of relicensing have had a previous claim that wouldn't happen, so I wouldn't assign too much weighting to that (if anything, it should be a red flag to look into what the IP situation is).
I think there are a bunch of questions you can ask:
* Why is the software open source (if licensing/contractual requirements make it so, that's more likely to keep the status quo vs. corporate claims of "we <heart> open source")?
* Who owns the copyright/IP (and what's their reputation)?
* What would happen if the the license changes (is there an ecosystem that relies on it being open source, or is it a black box)?
* Who cares what the license is (e.g. BerkeleyDB was relicensed, which got old versions frozen in linux distributions, so no-one upgraded to newer versions, and replacements were written)?