Compiler fails to find instances (master) / crashes (itask)

The attached program (main module is interpretergen) fails to compile while I believe it should. The current master compiler gives:

Overloading error [target.icl,491,;491;70]: "to_hword" no instance available of type a

The itask compiler:

(THWord.0M:0 [], t)
bindAndAdjustAttrs: incompatible types (1)

The offending line is target.icl:492, where I already tried to hint the type to the compiler using the ::: which should be superfluous.

There is one more issue, perhaps related: in interpretergen.icl, there are several cases where overloading could not be resolved. I marked these with NB:. I believe, for instance, that grow_a (to_hword n_a) on line 2174 should be allowed to be grow_a n_a because the type of n_a is known due to new_local on line 2164.