Twitter beat revenue estimates for Q4, the company announced Thursday, but it wasn’t all good news.

User growth fell short of expectations, with the social media site adding only four million users in the last three months of 2014, taking the total to 288 million. The figure marked an increase of just 1.4 percent on Q3, the smallest growth rate the company has ever reported.

However, following the publication of the figures, CEO Dick Costolo and CFO Anthony Noto said in an earnings call that issues with iOS 8 were partly to blame for the slow growth.

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The pair said that differences between iOS 7 and iOS 8, which was rolled out to users of Apple’s mobile devices last September, meant Twitter “lost four million monthly active users.”

So how does that work? Well, three million were apparently lost after Apple altered the way a Safari feature called ‘shared links’ works. This is a tab in the bookmarks section that lets users with Twitter accounts view a list of links posted in tweets by people they follow.

In iOS 7, Safari automatically connected with Twitter to pull the latest links, whether or not you hit the tab in Safari. Twitter calls this “auto-polling,” and, up to the launch of iOS 8, counted each of the devices where auto-polling occurred as a monthly active user.

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Why up to iOS 8? Because the latest version of Apple’s mobile operating system has dropped auto-polling, meaning new links are only pulled when a user hits the tab in bookmarks. The result of this change? A loss of four million users, according to Costolo and Noto.

Of course, many will argue that in light of this development the current figure of 288 million is actually a more accurate representation of the size of the service’s user base, and that it was unreasonable to include auto-polling in the numbers.

Regarding the other one million “lost” users, Costolo mentioned “an unforeseen bug” in iOS 8 that’s now been dealt with, though the CEO said the complexity of the problem means it’s taking time to get all the affected users back.

‘Great relationship’

Keen to avoid upsetting the Cupertino tech giant after apparently blaming it for the loss of some of its users, the Twitter boss said his company enjoys “a great relationship” with Apple.

Twitter on Thursday moved to reassure investors on the issue of user numbers, saying it expects to attract between 13 million and 16 million new users in Q1. This may, on the face of it, seem like an ambitious figure, though it’s similar to increases in most quarters across the last couple of years.