Bug on ui-percentage-mask="0" and ui-percentage-mask="1"

I've tested on 1.4.2 with angular 1.2.28 this bug also appears on demo page percentage mask...
When I use BACKSPACE to delete the values with the mask digits set to "0" I can not delete the last record, in the others masks, normally it is set to 0.

When the mask decimals is set to "1" when I backspace the last digit, the model value is set to NaN.

This repo is awsome I'm trying to figure out how to solve this, but I'm a dumb...

Thanks anyway.
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Reproduce both cases on the demo page with AngularJS 1.2.28: backspace with the percentage mask digits set to "0", and with decimals set to "1". Trace the percentage-mask input handling and model updates; done means the final digit can be removed in the first case and deleting the last decimal does not set the model to NaN.

Written by the indexing model from the issue text.