Microsoft has said it is working to speed up the time it takes for apps to be approved and published on the Windows Marketplace app store, after developers complained about slowdowns to the process.

With reports that the App Hub service, which developers submit their apps through, has slowed down and the average turnaround for app certification increasing by a day since January, Microsoft has concluded that the issues reflect “growing pains”, related to the increase in apps and markets supported.

Microsoft’s Todd Brix wrote on the Windows Phone blog post that short-term measures have already been taken to support the current service, with additional server capacity being put in place and the approval and publishing process being streamlined.

This work has seen average app certification times drop to 2.6 business days, a half-day improvement compared to 10 days ago. Bug fixes for App Hub have also been deployed to improve responsiveness.

In the longer term, the company is developing a “more robust and scalable” Marketplace service to address the current problems and support further growth. This work will be completed by late summer.

The number of apps in Marketplace increased by 60 percent in the first three months of 2012, with the total now approaching 80,000 apps. The number of individual Windows Marketplace app stores has doubled over the same period to cover 54 markets. “The addition of so many new markets and apps so quickly has slowed our backend systems,” said Brix.