It seems to be for me that if I order a lab and order somthing for the new tech level before the lab is built, but then order a research of a lower tech, when the lab is finished it will immedtately switch to the higher level one from the lower level one, done or not. But it will finish eventully, just after the topics that you ordered before are done.
Example:
T1 T2
- -
Order of research T2,T1
You have only one lab finished, but 2 have been ordered.
Since T1 is ready to start already but the others aren't it starts T1
But at 50% the Second Lab is finished so it stops T1 to work on T2.
When T2 is finished THEN it will resume on T1.
But if you say have a long line of T2 stuff ordered before T1, then it will seem as T1 froze because you have so many T2 ordered, thus making T1 wait for a long period of time.
But at higher techs research times are much longer so the T1 topic will be waiting a very long time. (could be 10 or more minutes, depends on how much stuff is in line before it.)
To see where the topic that froze is in line, hover your mouse over the research button and find where it is, and what is above it.
Off Topic:
While talking about research, I found a minor bug with the research time, while the first 2 or 3% are finished in about 0.1 seconds and then the topic slows down to a much slower rate. (But it doesn't effect the research time much, maybe 2 seconds on the T8 topics)