There might have been a recent regression, the parameter
deleteUnapprovedReportsOnApplicationStart has been introduced in 3.2 with a default behavior set to discard unapproved reports on app start.
Anyway, the deleteIntent method should be more efficient in doing this task. This is something I have to fix in ACRA's source, or you can contribute a patch via a pull request if you fill like doing it yourself.
I can't promise any deadline for ACRA updates as this is a spare time activity for me. I'll do my best.
Kevin