I can't seem to pitch slide down with the E command on a sample. Perhaps my track is too fast but if that's the case then that's unfortunate since it works with other tempos. Here is a link to see a video of the issue:
https://drive.google.com/file/d/1dLwJzfbA6RNNGhMRg1QFUNhc3bP9oWDJ/view?usp=sharing (https://drive.google.com/file/d/1dLwJzfbA6RNNGhMRg1QFUNhc3bP9oWDJ/view?usp=sharing)
Well I was able to resolve it by adjusting the tick speed to 2 instead of one. I don't remember having to do this before ;D
All slide commands, except for "fine" and "extra-fine" slides, are executed on all ticks but the first. Since there is only a "first" tick at speed 1, the slide will not do anything. Some very old OpenMPT versions also executed slides at speed 1 if I remember correctly, but that behaviour is wrong (incompatible with other trackers).