It's probably because of the size of the needle. The stitches have to stretch quite a bit from the cord to get onto the size 13 needle, and that can be difficult, especially for a yarn that doesn't slide easily on the needle.
"Trust the pattern!"
Time flies like an arrow, but fruit flies like a banana.
Hop aboard while we follow the cloud-covered van of knitting harmony, man!! Woooo!! --Hedgehog
IngridKH on Ravelry