Run this test: nested_seq, but turn on Debugger.withDebugger so you can see the trace information.

The array position advances faster than the byte position, meaning we're getting more array elements than bytes. Can't happen in textual data.

So that means somebody is advancing array position when it shouldn't be advanced so that it is increasing too fast.

Right now this bug doesn't seem to be bothering anything, but there will be functions in the expression language which expose this value, and also it's very misleading in the trace information.