I think I recall this in the past. After a battle with the Kaek, I gained class III shields from them, on the exact turn where my own research was completed and class III shields were next in queue to be researched. Now, even though I have the tech, I can't deselect researching it. Save attached
Thanks for reporting this issue and special case. In the meantime, resetting the tech queue (button in the top right of the research screen) cleans this (tech is deselected from being researched) and works as a workaround.