This is probably not likely but are we looking at other factors too? However unlikely it may be some of the strangest things interact very oddly with each other an it may be a combination of multiple things.
As an offhand example, Gnome rogues speak and understand Draconian; neither Gnome nor rogue has anything to do with languages but it's just bugged that way. Posting Race/Faction, specific talent spec, and maybe even items with specific proc effects might prove useful.
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Oh and one more bug about Killing Spree if it hasn't been mentioned already. Because you apparently phase during the duration, your focus will be lost when you use killing spree and you leave the phase of your target (I observed and tested this multiple times with another rogue I was swapping Tricks of the Trade with last night).
Set focus, pop Killing Spree, focus lost.
