It would be nice to have non-intrusive warnings in the sample editor if samples may cause trouble in one way or another, in particular in the MOD format (sorted by approximate severity, in case only one warning can shown it should be most severe):

• Samples longer than 131070 samples, will be trimmed
• Loop start 0, loop end < sample length (issue with ProTracker one-shot loop behaviour not emulated consistently)
• Warn about odd loop points / sample length

For XM the same could be done about finetune values that have the lowest 3 bits set, and maybe stereo samples being a hack.

I think these issues are not fatal enough to warrant a message box when saving the file, especially since some of these are just warnings about potential incompatibilities. Hence we should find a non-intrusive way to show these warnings in the sample editor. Maybe an icon + text in the toolbar right above the sample view? This might harm accessibility though as it's not a standard Windows control.