How to fight against disguised and treacherous 0-length linedefs?

Maybe you know it, maybe not. When editing a map, if you move a verticle on another verticle and you have bad luck and editor mysteriously fails to check for this, it may lead to creation of 0-length linedef. Linedef that connects two verticles with the exactly same position. This linedef is not just very very hard to find and remove, but also may cause problems with your map.
It's no joke. This occured to me several times in the past. They're especially annoying if they don't have set a texture and DB2 error checker reports an error, but isn't able to show where it is.
Yesterday I was making a vanilla map, tested it in Chocolate Doom and didn't notice any problems. Then I decided to playtest it again in Zandronum, just because. And when the map loaded and everything seemed fine, I opened the console to activate cheats. And only because of this, I noticed warning message that told me something like:

Linidef 9121 has been removed.
The map contains 1 0-length sidedef.

To remove it, I had to block-select all linedefs in the certain map section, then click-by-click remove all of them from the selection and then press delete. And after that, I had to redraw adjoining sectors to that linedef, because HOMs started to appear in my map in Chocolate Doom (but not Zandronum).

So I'm asking, is this a well known problem which is easy to solve, or did I discover something new?

(And if some of you have doubts, I'm emphasizing that this thread is no joke.)

Use a decent editor (like Doombuilder) which fixes these things automatically.

I use Doom Builder 2 which fixes these things automatically - but only with 99% probability, it seems. This happens just very rarely.

It might be related to one of my pet hates - the overlapping linedef. What you could try is to search for the linedef by its index number, switch to vertex mode and jiggle the offending vertex a bit, which should result in it stitching properly and the 0-length line being deleted.

What editor are you using?

He just said Doom Builder 2 in two different posts.

I've heard that WadAuthor is better at detecting stuff like this.

scifista42 said:

but also may cause problems with your map.

Any examples? :)

@Memfis: I've mentioned HOMs and flaws of DB2 Map Analysis (well, well, the HOMs appeared after I had removed the linedef). But I've already experienced that a single linedef can cause a crash of vanilla Doom. For example if it's middle texture is "submerged" into the sky or is multipatched. It wouldn't be good if this linedef couldn't be found and edited/removed. But OK, OK, these examples aren't maybe adequate. I must admit, I'm just a big perfectionist who cannot stand error messages :p
I'm not going to use WadAuthor because it's not freeware and also I cannot live without Visual Mode. :)

@GreyGhost: It might work. ZDoom based ports fortunately seem to detect these linedefs and also report their indexes. It took me a while to figure out how to search for linedef by its index (or even display the index), but now I know. Thank you!
Overlapping linedefs are also a tricky thing, but in most cases you can fix them by merging + redrawing sectors, because you know where they are, right? Whereas 0-length linedefs aren't clearly visible. But if you know where they are, then it's easy (easier) to get rid of them.

I'm not suggesting to completely swithch to WadAuthor, just that you could use its error check system when you need to find a 0-length linedef.

And I think when WadAuthor expires you can simply extract it in a new folder and it should work for the next 15 days just fine. :) If you're okay with doing that...

Memfis said:

And I think when WadAuthor expires you can simply extract it in a new folder and it should work for the next 15 days just fine. :)

Or lay your hands on a copy of the 3D Game Alchemy CD, which contains a registered version.