QProcess::readAllStandardOutput() and QProcess::readAllStandardError() returns output only first time

When I run my test script I notice that I can get valid output only when I call:

QProcess::readAllStandardOutput()

QProcess::readAllStandardError()

first time. Any subsequent calls are empty. I read carefuly documentation of these functions but I don't find any mention about such behaviour. I suppose that this can be valid when we use QProcess::waitForFinished(XXX) in some small XXX and read partial results from output of sub process. But where there is some info about this?

I attach minimal working example of this behaviour.

Please update documentation or fix QProcess.

Thank you for great job!