Using 8.91, speed change -slow and fast - was tested and succeeded on several files. There have been no other reports of it failing, to my recollection.
That version is dated, but you shouldn't have to pay for any release that falls within the six-month grace period since your purchase. Download here. Ignore any virus warnings. A bug in your version, which doesn't appear to be the case here, may have been fixed within that period.
Newer versions can also be test driven for a trial period, even if not licensed. There's a limited feature free version available here.