TZUTC: -0700   
   MSGID: 56255.sync_sys@1:103/705 2b41edbb   
   PID: Synchronet 3.20a-Linux master/e93b6dfa6 Aug 22 202 GCC 12.2.0   
   TID: SBBSecho 3.20-Linux master/984c371ae Sep 06 2024 20:48 GCC 12.2.0   
   BBSID: VERT   
   CHRS: ASCII 1   
   https://gitlab.synchro.net/main/sbbs/-/issues/782#note_5571   
      
   I looked through some old commits and found [this](https://gitla   
   .synchro.net/main/sbbs/-/merge_requests/237#note_2998), which is where I   
   encountered and worked around a similar issue.   
      
   Looking at the two commits there, it seems that maybe:   
   - computing an array index inside the accessor is sometimes problematic?   
   (`array[somevalue + someothervalue]`)   
   - introducing a situation where the dynamic index value might be coerced to   
   string / passed into log() will make it become real?   
      
   You might try changing:   
      
   ```js   
                               if (FFrameMasked) InByte ^= FFrameMa   
   k[FFramePayloadReceived++ % 4];   
   ```   
      
   to   
      
   ```js   
                               var idx = FFramePayloadReceived++ % 4;   
                               if (FFrameMasked) InByte ^= FFrameMask[idx];   
   ```   
      
   or even   
      
   ```js   
                               var idx = FFramePayloadReceived++ % 4;   
                               if (idx < 0 || idx >= 4) log(LOG_DEBUG, 'idx is '   
   + idx + '(this will never happen)');   
                               if (FFrameMasked) InByte ^= FFrameMask[idx];   
   ```   
      
   which seems similar to what I ended up doing. Which of course would be a   
   workaround but I wonder if either of those would "solve" the problem.   
      
   Regarding JS runtime behavior, it's wild speculation on my part. I remember   
   seeing discussion within the past few years of what I think were compile-time   
   options for SpiderMonkey and something in that is nagging at me, like this   
   could be a symptom of some JS optimization gone wrong.   
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