If one of the settings goes too high( or low? I can't recall which) that occurs at the transition between land and ocean. I used to know which one, but can't remember anymore. Seems like someone pointed out it was a bug, but again don't recall for sure.
Right, and this occurs because when the depth of a biome times biome depth weight and plus biome depth offset exceeds -2 it causes the results of a calculation to reverse in sign, which causes the odd terrain generation at the boundary of (initially) deep ocean. Since deep ocean has a depth of -1.8 this means that the spikes to start to appear at BDW of 1.111 (at first the spikes extend downwards before going up at around 1.125):
Regular ocean has a depth of -1 so a value of 2 will cause the same thing around oceans, and for river biomes, whose depth is -0.5, the value is 4. Note that since biome depth offset is added after the depth is multiplied by BDW this means that increasing BDO will prevent the spikes from occurring. For the OP's BDW setting BDO would have to be at least 0.2824 to avoid any signs of the bug.
While this may have been unintended when it was first implemented, and if the results of the calculation are exactly 0 the game will crash (division by zero, though since float values are used it is unlikely to ever be exactly 0, but very large numbers result when it is close to 0, hence the spikes), Mojang actually considers this to be a feature now. In order to increase the range of biome depth without causing this issue you can increase BDO and decrease depth base size, which will offset each other so biomes with a depth near zero will still be near sea level (the default DBS of 8.5 results in zero height being y=68).