Some questions do arise from this combination. D10 has been described as normally used for fiscal purposes. This may prove that it was used postally as well. Conversly, one could also infer that bar cancellations were also in use fiscally.
The stamp itself has an interesting flaw/dot next the letter A in postage.
A violet Kudat D3 and adjacent to it probably an arrival/transit marking with the letters "age".
It was probably used in Brunei. There was bound to be some leeway in the use of stamps from adjacent countries. But it is unlikely to be that common.