This is yet to be verified by someone else, but it seems like I've managed to solve the problem with buckets not working properly with the latest version of the Manual Attach mod (184.108.40.206).
The problem seems to be introduced when the Manual Attach mod overwrites two functions "getCanDischargeToGround" and "getCanDischargeToObject". Within those two functions, the mod checks if the vehicle (and we should remember that the Hof Bergmann bucket is a "vehicle") is not a shovel (for skid steers, front loaders, etc.) and if the vehicle has attached hoses. If it is not a shovel and hoses are not attached, discharging from and to the vehicle is not possible. Sort of makes sense if you have a trailer and need hoses attached to unload. Not so much with the bucket. By adding one line of code to those two functions, the Manual Attach mod no longer applies these restrictions to HF buckets.
Here is how to fix it. You will have to add two lines of code to the Manual Attach mod file: "FS19_manualAttach/src/vehicle/ManualAttachConnectionHoses.lua":
the line of code to add: and not vehicle.type == "bucket"
Line 366, function ManualAttachConnectionHoses.inj_getCanDischargeToObject
Line 376, function ManualAttachConnectionHoses.inj_getCanDischargeToGround
Save the file, zip the mod and you should have the latest version of the Manual Attach mod working with functioning buckets. Please check if it works for you and let me know in the comments below.
Manual Attach mod has been created by Wopster, and this magnificent dude holds all the rights to it, so be mindful of that, if you think of redistributing the mod.