The content of the imported file would look like this if the import is not done from the root file.
391:[function(require,module,exports){
},{}]
So, if c is imported from b and I run browserify + tsify on b, all is fine. If c is imported from b and b is imported from a and I run browserify + tsify on a, c will be empty.
edit: Yeah, I think this explains it better: #148
The offending commit is this: a585084