I’ve noticed that with Homespun sometimes. It seems to vary from one skein to the next. It seems like sometimes it’s bound a little more loosely with the binder thread on some skeins. It could also be a trait of boucle yarn in general, but I’m not sure because I usually use just smooth yarns. But I am willing to bet that it’s the construction of the yarn that is making it so you can’t unbunch it.
I have noticed that knitting too tightly can make it worse with Homespun. I switched from 10 1/2 to 11 needles on a scarf that I was making and the bunching up problem quit.
Also, are you pulling from the center part of the skein? I’ve noticed that sometimes they come out of the center really tight. I think that when you’re pulling it out, it can stretch the yarn and then it bunches back up on itself. So you might try winding it into a couple of smaller balls. I agree with Tillie you don’t want to cut and then tie your yarn together, not only because of that yarns trait to “dissolve” when you cut it, but also because knots will create weak spots in your knitting and can also poke through to the sides where you don’t want them to show. If you absolutely have to cut the yarn, try cutting out the offending section, tie a knot at each cut end (which will help to prevent the yarn from unraveling). Knit with both the old end and new end together for a few stitches and then drop the old end. Later you will need to darn in the ends, and you will have to cut the knots off the dangling ends, but in the meantime, they won’t fall apart.
If it’s really truly frustrating you, though, but you want a nice thick yarn, Lion Brand makes some other yarns with gorgeous colors that knit up quickly–like Woolease Chunky and Woolease Thick and Quick.
Sorry for the novel!
Hope it helps though.