That claim is widespread indeed, as a quick google confirms. However, I could not find any scientific source with scholar google that supports it.
Maybe that this impression comes from some paleo biological studies and the tectonic history, as it has always being on lower lattitudes in that period. By the same token, however, we could have thought that of the Sahara
, had we lived ten thousand years ago.
So, with the apparant absence of a continuous fossil record of the last million years, it's equally likely that Malaysia also has been spending some time in the arid subsidence zones of the hadley cells
, that forms deserts like the Sahara. Maybe only a few thousend years, which would only seem a negliblible hiatus on 100 million years.