I was just setting an inserter enable/disable constant condition. I wanted to type 200. When I typed 20, a research (the last one in the queue if that matters) was finished and the input field lost its focus so the second 0 didn't make it to the input.
How to reproduce:
Start a research.
Click an inserter.
Enable the checkbox "Enable/disable".
Click the constant number (right value).
Make sure the number input has the focus.
Wait for the research to finish.
I consider this a bug because it hapened while I was typing and I got the wrong value due to the focus loss.