``` [...] startWaveform(GPIO, 100, 100, 200); delay(200); stopWaveform(); […] ``` Due to code in master branch, core_esp8266_waveform.cpp, `stopWaveform(uint8_t pin)`: ``` uint32_t mask = 1<<pin; if (!(waveformEnabled & mask)) { return false; // It's not running, nothing to do here } ``` the timer keeps running even when there isn't any other waveform or the callback attached. Fixed in #7022