It seems to appear when there are stacked pools and 1 of them is fished out. The bot detects the second pool at the same location and turns. Maybe the bot thinks he turns towards the same pool but its not. Its acually turning away and therefore casting the wrong way.
EDIT: Forget this it also does it with single pools.
18:29:13 - [Fisher] Fish Brackish Mixed School > 752,082 ; 7086,81 ; 18,2676 ; "None"
18:29:14 - [Fisher] Going to point > 759,7232 ; 7097,327 ; 20,12733 ; Flying
18:29:16 - [Mount] Dismount
[F] 18:29:18 - [Spell] Cast Fishing (Fishing)
[F] 18:29:20 - [Spell] Cast Fishing (Fishing)
[F] 18:29:23 - [Spell] Cast Fishing (Fishing)
[F] 18:29:48 - [Spell] Cast Fishing (Fishing)
[F] 18:29:50 - [Spell] Cast Fishing (Fishing)
[F] 18:29:52 - [Spell] Cast Fishing (Fishing)
[F] 18:30:12 - [Spell] Cast Fishing (Fishing)
[F] 18:30:14 - [Spell] Cast Fishing (Fishing)
18:30:21 - [Fisher] Fish Brackish Mixed School > 752,082 ; 7086,81 ; 18,2676 ; "None" <----- From here it turned the wrong way again.
18:30:21 - [Fisher] Going to point > 759,7232 ; 7097,327 ; 20,12733 ; None
[F] 18:30:25 - [Spell] Cast Fishing (Fishing)