Cannot update subscriptions with usage based addons

[ScottSpittle]

Now using subscriptions with usage-based addons I am unable to update those subscriptions.

New subscription with no addons with the following code works fine.

$subscription = Recurly_Subscription::get('[subscriptions_code]');
$subscription->quantity = 2;
$subscription->updateImmediately();     // Update immediately.

New subscription with on-demand addon with the following code does not work.

$subscription = Recurly_Subscription::get('[subscriptions_code]');
$subscription->quantity = 2;
$subscription->updateImmediately();     // Update immediately.

I get the following error, "The provided XML was invalid."

[bhelx]

@ScottSpittle thanks a lot for reporting with code. I'm going to try to reproduce this today and see what the problem might be.

[bhelx]

@ScottSpittle I've identified what the problem is here. I'm going to get a PR out for review today and will link back here.

[bhelx]

A quick update on this. I'm still looking at it but it's a little more delicate of a change than I initially thought. I hope to have something out today or tomorrow.

[bhelx]

@ScottSpittle It's in master now and will go out in the next release. Will ping back here on the release PR. Please feel free to re-open if you think the conversation needs to go on.