Timestamps automatically changing from desired time

Hello, I’m having some issues when inputting timestamps on keyframes.

When I select the timestamp checkbox, and input my time, it automatically alters what I entered. Initially, I thought this could be because another keyframe was set to this time, but that was not the case. Every time I entered, on any keyframe, got changed. I was wondering if there was a pattern to these changes, but after testing it, it seemed entirely random. For example, I set a keyframe for 00:01:30, which was changed into 00:01:25. I reentered 00:01:30 for it to be changed to 00:01:37. In each repeat, it was changed to a different time. It seems it will change to any time but the one I actually need.

Is there something I’m missing? Thanks very much.