Cushion - with Ink and Spindle fabric

I have never made a cushion cover before but wanted to use my lovely Ink and Spindle fabric (on the left - Bloem in white) for something around my home. I have two old brown suede-like cushions that needed freshening up - so this is the first cover I made. I did use a mis-matched weighted linen (because that is all I had) and it probably should have been the same weight but it turned out ok. I used Lara's tutorial (from I&S) on invisible zips as a quick tut for the cushion cover itself. The plain linen kept catching the little slubs as I sewed a straight line :-( Has anyone else had that problem? I did a quick search on Wiki and it did mention that slubs are actually defects associated with low quality linen (good to know) next time I buy some linen!!