Currently, Premiere Pro adds audio tracks to a sequence whenever a file with more audio tracks than the sequence contains is opened in the Source Monitor. So, say I have a sequence with four audio tracks. If I open a clip in the Source Monitor that has 8, four more tracks are automatically added to the Sequence. This is behavior is fine for the auto-generation of NEW sequences, but frustrating in that it modifies an existing sequence with no user input whatsoever. The functionality for adding tracks, as well as source patching and track targeting, works fine, and this behavior is more of a bug than a feature.