While the online map viewers only have a few limited categories – like OpenCycleMap for bicyclists – the offline map editors are able to show and hide different layers, if I’m not mistaken.

What I often do with stubborn ways is to first remove all their tags, then remove all but the last two points, then shift the focus somewhere else to get the changes to save. Then, once that happens, I delete the rest of the points.

Yes, they’re seriously addictive! Every time I get to a power station, I realize I’m going to be spending another couple hours mapping out power lines. I typically shy away from editing streets while mapping power lines, though, because in the U.S. most of the streets are taken care of -- shoddily -- by the TIGER import. Instead, I map nearby lakes and ponds, just as mindlessly as I map power lines, since it’s so easy. :^)

To delete a way in Potlatch, you need to click on the end of the way. Instead of extending the way by creating new points, press the Backspace key until the way disappears. Make sure you get rid of the very last point, too. If it's a very long way, you should periodically press Enter (to get out of way-editing mode) and click somewhere else on the map. By shifting the focus away from that way, you've saved it. Sometimes big edits like deleting a huge road can cause the road to magically reappear. Drives me nuts.

It turns out this time the problem was that, when I joined two of the river’s ways together, it simply overlaid the existing ways with another, longer way. That threw Osmarender way off.