Should you run into export irregularities when a global speed change has been made on numerous clips, try this...
Prior to applying the speed change, click the + sign on the Sequence 1 tab, to open a new blank sequence.
Click the SEQUENCES tab in the bin (upper-left). Right-click on Sequence 1 and PLACE ON SEQUENCE AT START.
This becomes a single clip. Add the speed change, then export Sequence 2.
Chances are you won't have to do this, but it's an alternative.