High callback timing error in VB-Audio ASIO Test

[dechamps]

VB-Audio ASIO Driver Tester currently looks like this in FlexASIO 1.10a with the default config:

That doesn't look great. Presumably this could affect timing/sync in ASIO host applications, or perhaps even cause glitches.

I suspect this problem has always been there and is not a regression. My best guess is this is a consequence of the way PortAudio buffer adaptation works - especially since this test is full duplex. That being said, maybe there are ways to improve on this, e.g. by strategically aligning buffer sizes, or by improving PortAudio's internal logic.