I'd just like to point out one thing here that may be of interest though. From the article Derek posted, several of the VTT's only supported it because the community wrote a script/importer/plugin.

Community effort is a great thing, and for a thing like this, maybe someone in the community would consider writing their own add-on to CC3+ to support this? Of course, this does require a bit of programming, but if C++ doesn't scare you, all you need to get started is here:

One should be able to gather more or less all the information needed by walking the drawing list and process the values.

After making the map, you can use View -> Move Origin to put the 0,0 wherever you want. I recommend turning on snap and cursor snap to make placing it in the exact center more easily

The fills for the DD3 corridor/room tools unfortunately cannot be set via the style, so they will always be the same as last time you use them. You need to manually just pick different options in those fill style boxes before using those tools in a new map. Only fills from the current style should be listed there.

Basically two ways to handle it:

• Don't start in a corner, start in the middle of a side length. As long as the starting and ending point is the same (as well as the angle of the two segments) it will meet up seamlessly.
• Turn it into a polygon. Draw it as normal, but don't do the final connecting segment. The use Path to Poly [CLOSEPATH] on the wall you just drew.

This is basically the way to handle this when you try to draw a closed shape with a line-type drawing tool, being city wall or dungeon room.

Have you tried running the latest update (Update 28) available from your registration page? Even if your CC3+ install is already at 3.98, the update fixes up other files in addition to the core program files, and can often fix weird issues like this. It is usually a good idea to install it as a last step after installing all add-ons (except the free monthly symbol sets, they should be the very last)

If that doesn't work, I recommend getting in contact with tech support, also available from your registration page.