iPhone's dictation doesn't work with Description field

iPhone's dictation doesn't work with Description field

Hello,

We've found that the iPhone's dictation function doesn't work with the Description field, but does work with the Subject field. Two questions:
1) Is this a bug, or by design?
2) Is there a character limitation in the Subject field?

We've tested this on two separate iPhone 4Ss, using Zoho CRM version 2.1 with the most recent iOS software (6.1.3)

Thank you.