Is it normal for collaborator to rerun experiments himself? So I'm a few months into my PhD. It's built on top of previous work that has not been published. My supervisors, collaborators, and myself are working on to get this published. Now here's where things get a bit weird for me.

I found some problem with the previous work. Discussed the problem with my supervisors and have fixed them. For the publication, I'll need to redo the experiment.

So far I'm not getting a satisfactory result as it's tricky to get right. Not gonna go into why, it's just tricky.
My collaborator has been impatient with the result I'm getting. So now he has decided to rerun the experiment himself and double checking that he's getting the result I'm getting. Turns out it's quite similar. So now he's trying his own idea he has only briefly disclosed to me and one of my supervisor. When asked indirectly why he's doing this, he said he's just trying to understand the experiment better.

I found this disturbing. Why are you repeating my experiment yourself only to come and tell me you found exactly the same problem and result?

What's everyone take on this? I would like others opinions first before I discuss the issue with my supervisors.
I don't find that behavior strange at all. If I want to understand problems with algorithms (I don't do experiments with anything other than algorithms) I need to run them by myself and sometimes even implement the method from scratch. It's not that I do not trust other people's code, but if I want to understand all the mechanisms well, it's much easier to get a grip on it when I've done it myself.

The other way round, I do not have any objections if a coauthor of mine re-implements a method I already provided just to see how it works. On the contrary: Usually I benefit from this in one way or another, e.g. by learning new tricks or getting rid of bad programming style…