Note this paragraph from my debugging page in the wiki.
This may be what is happening.

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I worked on one site that added its own toString() functions to various prototypes, and these in turn had trace points,
so when I asked for the value of x, and it tried to turn x into a string, it entered the toString() function associated with x, which triggered more breakpoints, which was really really confusing.
I entered . . . and finally got back to the string value of x.
I hope this is a rare occurrence.

Karl Dahlke