Melanie,
RGBM has three factors that change the population of bubbles if you do bounce dives, reverse profiles, or repetitive dives (see “Decompression Theory” by B.R. Wienke). RGBM keeps the volume of gas in bubbles below a threshold value by controlling pressure gradient (difference between dissolved gas pressure and ambient pressure) and time. If you have more bubbles due to doing a bounce you get to that critical volume of gas faster. Dr. Wienke, to my knowledge, has not publicly disclosed how the calculated number of seed bubbles changes with bounces, reverse profiles or repetitive dives. Nor have those factors, again to my knowledge, been validated. So it is hard to answer the question what happened with your dive. Although it does sound like the conservative factor associated with bounce dives may have come into play. Following a computer that does unpredictable thing is no way to execute a dive that needs planning. You and your buddy really need to be following the same plan and as you have learned your computer is not helpful for that.
By the way I too was alarmed about your dive. We often do not realize the risks we are taking while diving because we get away with it most of the time.