J.R.
Yep, I have this problem sometimes too, though I haven't associated it to any particular foods. sometimes he just wants to be on the go and eating is 'boring' i guess. I also think my son may be slightly claustrophobic (Dad has a case of it too) :) even inutero he seemed a little anxious to get out... he HATED being swaddled and doesn't like being confined in his chair... he isn't terribly fond of his car seat either so I really think he just doesn't like the confinement sometimes :)
At 18 months I feel it's a bit early to move him to a regular chair, but we're leaning that way soon.
Maybe your daughter is just more content to be confined in the chair, when what she's doing keeps her distracted. baby corn is, after all, fun for the whole family... :) my older kids (10 & 12) still seem fascinated by them! hahaha