I ran into a problem where continue did not work properly with an imageinfo query:
https://commons.wikimedia.org/w/api.php?action=query&continue=&format=json&iilimit=50&iiprop=url&iiurlheight=480&pageids=3982584|3982588|3982595|3982603|3982606|3982617|3982634|3982639|3987381|3988044|3988237|3988332|3988424|3988480|3991285|3992308|3992901|3992908|3992939|3993018|3994073|3994076|3994083|3994195|3994505|3994506|3994508|3994510|3994584|3994630|3994692|3997992|4016017|4030078|4030104|4030351|4031166|4033567|4034071|4034081|4034085|4039921|4040180|4040191|4040194|4040220|4040222|4048502|4051075|4068154&prop=imageinfo
The first query returns this : {"continue":{"iicontinue":"Barack_Obama.jpg|20081103215509","continue":"||"}
The second query returns this: {"continue":{"iicontinue":"Barack_Obama.jpg|20080913075003","continue":"||"}
After that, using the second continue returns the same data and continue value again (and again and again).
https://commons.wikimedia.org/w/api.php?action=query&continue=&iicontinue=Barack_Obama.jpg|20080913075003&format=json&iilimit=50&iiprop=url&iiurlheight=480&pageids=3982584|3982588|3982595|3982603|3982606|3982617|3982634|3982639|3987381|3988044|3988237|3988332|3988424|3988480|3991285|3992308|3992901|3992908|3992939|3993018|3994073|3994076|3994083|3994195|3994505|3994506|3994508|3994510|3994584|3994630|3994692|3997992|4016017|4030078|4030104|4030351|4031166|4033567|4034071|4034081|4034085|4039921|4040180|4040191|4040194|4040220|4040222|4048502|4051075|4068154&prop=imageinfo