When I added the above URL to M9 (build 126.96.36.199) the URL now looks like this:
When I copy and paste any strings into the Source box of a New Data Source dialog set to "wms" in the Type box, the dialog does not change the URL at all.
I think what is going on is that by your phrase above you don't mean that the New Data Source dialog makes any changes. It takes exactly what you enter as you enter it. Instead, I'm guessing that after you create the data source, if you then right-click onto that data source in the Project pane and look into the Properties, you'll see a JSON string that escapes special characters. That's correct, and exactly how it is supposed to work.
The JSON text string in the property has to work within other processes, such as SQL expressions, that use it. In such cases you have to escape special characters (a forward slash is a special character) with the backslash character. But that's a different situation than entering free text into a "Source" box for a URL, or entering such text into a browser URL box.
WMS works fine. If you'd like to test many different WMS services, visit the Product Downloads page for 9 and download the JOSM sources example map from the list of examples. There are many wms servers in there, for example, under Canada the Canvec server that provides an SCW-Toporama image.
As to why a particular server doesn't work for you, there is useful discussion in the Web Servers topic Notes section. There also have been threads in this forum on why, for example, Google might be blacklisting you (too much use, you're not using a free developer account, etc.). Classic problems with WMS is that WMS servers are routinely misconfigured, they aren't working (shut off for maintenance or just turned off), the URL changed and the webmaster didn't tell anybody but his friends, somebody in the bureaucracy decided the server was getting too much use so they now require access credentials, or they are just inconveniently configured. The WMS URL you provide is a classic example of the latter.
The particular WMS server URL you provided works fine, it's just very slow and it only provides layers when you zoom far in. Do this:
1. Make a data source for it.
2. Create a default Bing streets data source from the Favorites.
3. Create a new map and open it.
4. Drag and drop the Bing layer into the map.
5. Zoom into Vancouver, Canada.
6. Drag and drop the pub:WHSE_CADASTRE.PMBC_PARCEL_FABRIC_POLY_SVW Image layer from your data source into the map, as a layer above Bing.
7. Zoom far into the street grid of Vancouver, so you see approximately five city blocks wide by five high in the display.
8. The DataBC layer will fill in and appear. I'm using it from Europe so maybe that adds slowness.
Why it is that webmasters configure WMS services so they show nothing until you zoom far in? Good question for the webmaster publishing that server.