Net amount being calculated incorrectly

[Matt-WF]

Hey folks,

I've got 2 issues that I've been able to recreate on the drupal.demo installation and one a bit of an odd one. They may not be bugs and I may just need clarification on the usage of these fields.

Steps:
Contributions > New contribution

1. Select donation (unsure if "donation" is related) and GBP as the currency
2. Enter an amount of 467.77 into the 'Total Amount' field
3. Scroll down to Additional details and enter 16.10 in the 'Fee amount' field
4. Enter 451.67 into the 'Net amount' field
5. Try to save

Error shown is "Please enter a valid monetary value for Net Amount."

Second issue:
If you repeat the steps above until step 3 and then hit Tab, Civi calculates the value for the Net amount as 451.66999999999996; rather than 451.67.

Could anyone shed any light on this?

Thanks,

Matt