This is a known bug. Please download and install the latest beta version from the beta 4.3 thread.
How are these buttons configured? Also, please enable extended logging, reproduce the situation in which the VU level maxes out, then click the āUpload logā button, and attach the log ID to your answer.
Follow the āBeta version 4.3ā thread in the Beta version forum to the end, and download the latest version linked in that thread.
I donāt know which track maxes out, but I canāt see anything wrong in the log file.
The VU information in Mackie Control is very crude and only shows 12 levels, so the level in the plugin is not an exact replica of the level in Reaper. The plugin shows the values sent by Reaper. If those values are not explained by this 12-level approximation, the problem lies in Reaper; the plugin cannot (or rather should not) show anything other than what is sent by the DAW.
Fader design has nothing to do with it. If the DAW sends the max value of 12 for the VU level (as I can see in the log file that Reaper does), the plugin will show the VU meter maxed out regardless of which design you have selected.
If you tell me which track is maxed out, I can show you the values sent from Reaper.