I have written a template extension 

<template id="moduleA.custom_template" name="Custom Template" inherit_id="moduleB.template_id">
    <xpath expr="." position="inside">
        <div>hello</div>
    </xpath>
</template>

But this somehow inherits the base template for actions with id: 'base.action_view'...
I have added moduleB to the dependencies in moduleA

I have already managed to extend template 'moduleB.template_id' in another one of my modules. If I put this template in that module it just works.  

I don't see a difference in the modules as to why it shouldn't work, let alone inherit a different template than specified...