I didn't understand that decision back then and I don't understand it today. The patch weighs in at about 100 lines which doesn't seem heavy to me. Especially when you consider that without the patch the bootstrap-"modal" is not a modal...
Anyway, here's the fixed bootstrap-modal.js for the version that was current back then:
https://gist.github.com/0d04646ab6cf4df50610
Line 23-82 is the important bit, that snippet is lifted nearly 1:1 from jquery.ui.dialog which fixed this issue ages ago. Beyond that there's only a couple lines of glue code.
Feel free to port this forward to the current version (or better-modal). Personally I've stopped using the javascript parts of bootstrap because I don't want to maintain forks for basic bugs like that.