Non-deductible field in Contribution record is not always populated correctly when Staff uses: + Submit Credit Card Contribution button

when Staff uses: + Submit Credit Card Contribution button (so processing a Credit Card transaction off-line via CiviCRM) we see many records in which: non-deductible amount = Full amount even though Contribution Type (in CiviCRM admin settings) is properly set to is deductible.

I have seen this on a 4.2.6/Moneris and on a 4.2.7/PayPal pro site - on the 4.2.6/Moneris we're seeing non-deductible = Full Amount [incorrectly] in almost always 90% of the cases [even same $amount, same staff person, same contribution type, same event fee code - same day entry]. We can reproduce things fairly consistently here. On the less busier 4.2.7/PayPal site we're seeing this in roughly 50% of the cases.

The non-deductible field is critical to anyone using it for tax receipt purposes. Currently we have e.g. two $500 donations of the exact same type and fee code - processed the exact same way - by the same staff person - only 18min apart and one will get a $500 tax receipt - and the other will not get any tax receipt b/c the non-deductible amount is $500. The easy bandaid fix is to import non-deductible amounts of $0 into the 2012 contributions that are 100% eligible - but obviously we need to get to the bottom of this.

I'll commit to digging into this. Any thoughts are to what may be happening here - most welcome.