I2C software baud rates much different from hardware baud rates

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What steps will reproduce the problem?
1. Select I2C, Hardware, 400KHz, turn on power and pullup, internal 3.3v
2. connect one slave device, (0) to search bus, reports slave address
3. Mode back to I2C, Software, ~400KHz, power and internal 3.3v pullup on
4. same slave, connection not disturbed, (0) finds no slaves.
5. Return to Hardware I2C, (0) finds slave again.

What is the expected output? What do you see instead?
Expect to be able to find slave with either I2C mode.

What version of the product are you using? On what operating system?
Bus Pirate V4, v6.1 thru v6.3-beta1 r2151

Please provide any additional information below.
In software I2C ~400KHz, oscilloscope shows CLK period is 8.2uS, rather than 
the ~2.7uS when run in hardware I2C 400KHz.

Original issue reported on code.google.com by [email protected] on 12 Mar 2014 at 6:07