Rendering Envelope Problem

I’m running Audacity 2.1.2 under Windows 7. Editing bad acoustics in a cassette recording ~30 min long, I’ve reduced the magnitude of a number of clanks/clicks using the envelope tool to dip the envelope briefly when the noise occurs. Then running Tracks/Mix and Render results in vertical full-height red lines at every fix, the kind I usually see when clipping is detected. Anybody got any suggestions about what the problem is and/or how to fix or evade it? - Bill Fisher

Checking the suggestion that maybe I moved the envelope above the top of the display, I discovered that the red-line bars are not just where the envelope dips were. They seem to be at unusually loud places, which, however, never went above 0.5 on the 0-1.0 vertical scale, have a flat envelope at 1.0, and are not tagged as clipped before the rendering.