I assumed that every regular timeframe has regular timestamps, and candles from a fine timeframe do not cross boundary of the coarser timeframe (except month timeframe, which is incompatible with this rule).
But some brokers do not follow this assumption, breaking the rule occasionally (like in the picture) or systematically (like aligning candle timestamps to xx:15, or H4 candles to 03:00, 07:000 etc.) Some even have different date between current D1 and H1 candles (D1 lagging one calendar day for a few hours in the day).
Is the MT4 intended to allow such irregular charts?
And how to treat those irregularities? (i.e. how to detect them when traversing between timeframes).
Ok, I take the silence as yes, any mess is allowed with MT4 charts, and custom checks are inevitable for serious coding.