This is usually not the case with coal tar. In my experience sealer cracking can be explained by three main reasons. First, if newly laid asphalt is not allowed to fully cure and a sealcoating or barrier coating is placed on the asphalt, the coating and subsequently the asphalt will prematurely age, shrink, and cause this cracking. The second reason is when multiple layers of sealer are installed on a driveway for instance over a period of years. The bottom layer ages and shrinks.
Cracks develop and water seeps in to cracks submitting the coating to the freeze thaw cycles.
Eventually the coating loses adhesion and begins popping off. The third reason is improper compaction by the paving contractor. If the asphalt is not fully compacted it remains too flexible. The movement caused as vehicles travel across the pavement leads to cracking of the coating as the coating cannot flex. Other reasons may exist but these are the most prevalent.