I'm having the same problem in InfoPath 2007 as this user. Essentially, new sections added in a repeating section have some controls disabled.
The first section of the repeating behaves as expected. Then in the next section added, fields such as AmountReceived will work fine but FeeType and NoFee will be disabled.

There is no conditional formatting on these fields. Nothing appears unusual in myschema.xsd although I’m not really sure what to look for. There is no code behind.
Any ideas greatly appreciated!
Thank you,
Alex.