Hello Jennifer,
Thank you for reporting this. As a temporary workaround, you can re-add the snipe using the Add Snipe box. You don't have to delete the snipe and add it again, you can just use Add Snipe with the new value.
Now as for the problem itself, do you have a moment to try another browser, to change a bid amount? This way, we can rule out any problem that is browser-specific. Then I can try to reproduce the problem on our side.
Let me know and I will watch for your e-mail.
bidslammer