Nah, it's not just you. I first ran into this way back when we were just starting to work on Scareplane. Unfortunately, I never found an easy way to detect negative keyframes or a way to easily delete them. After that incident, I just grew careful not to let that happen again.
But despite my care, recently I somehow moved a bunch of keys over into the negative frames area and it took me quite a while to isolate the layers and channels where this happened. Like you, I could only do this by dragging each layer forward in time (in the Sequencer), and moving or deleting any negative keyframes that may appear, and then moving the timeline back to it's normal start position. It's pretty annoying because you don't really know if you're dragging the layer far enough in time to see all the keyframes, and if you think maybe you had not, you have to start over again. (Which makes me wonder, what's the point of having a separate clear from layer command when the other one is specifically for frames after 0?)
To me, the obvious workflow would be to copy the keyframes I want to keep, use the Clear Animation from Layer command, and then paste the 'good' keyframes back in where I want them--simple and straightforward. Unfortunately, negative frames appear to be protected from deletion.
In my case, I think this situation can happen because I'm constantly importing items and groups from other scenes, which also brings in the keyframes from those scene. If I off-set the layers without considering existing keys, they can get pushed into the negative zone and forgotten about until they cause a problem--then, it's just really annoying to delete them.
I wish I could just scroll the timeline over to negative frames to see what's over there like in other animation programs. Since 'setup' in ASP is done in frame '0'. I guess I can understand why the devs want to hide negative frames from the user but personally I think that should be optional.
Anyway, I know that's not a lot of help but maybe it's a little consolation to know you're not alone. For me, luckily this happens very rarely but when it does, ugh!
G.