Am having a bit of trouble with my ditches

Problem 1:
Several squares wouldn't let me draw the ditch even though they are next to water or next to a filled ditch ("You aren't quite sure what to do there"). I was able to draw a ditch on another nearby square that is not next to water or another ditch (but didn't bother digging it out)
Problem 2:
One square, next to water, where it did let me draw the ditch, I then dug it out to 30.1 cm, but then it said "You are almost finished, but alas, there is no water near your ditch! Maybe you should try to connect your ditch to a water source". The only reason I could think of is that the ditch goes north-south but the water is to the east. But I couldn't see a way to choose the direction of the ditch.
Problem 3:
This unfinished ditch isn't filling back in. I gather I can fill it with poo but my preference would be to leave it to disappear naturally.
I finally got success on another square, which has water on two sides, but that only gives me three squares to plant jute and I can't extend that ditch for the same reasons.
Am I doing anything wrong or is this bugged? Any help appreciated.