Disputes about Microsoft's anti-competitive browser bundling are still in full swing, even though the software giant said in July that it will no longer shield Internet Explorer (IE) from competition in Europe by bundling it with Windows.

Three competing browser developers have been working with the European Union's Competition Commission on the investigation into Microsoft's browser practices, and have now said that the firm's proposal to offer a ballot system for Windows users to select their default browser from a list is not good enough.

One of the problems is that Microsoft will offer the browser ballot from within IE, which Opera Software argues makes the other browsers look less important.

"The proposal on the table could work, but it needs some changes," said Håkon Wium Lie, Opera Software chief technology officer.

"We think it's important that the ballot screen is impartial. Therefore, we ask that the ballot screen is not run inside an IE window that has IE logos on it. In an election, you wouldn't accept that one candidate has his logo in the corner of the ballot, and it shouldn't be accepted in the ballot screen either.

"Likewise, we don't think voters should be warned against their candidate of choice when they vote. We are therefore asking that warning messages should not be shown to users who request non-IE browsers."

Opera Software initiated the European Commission's (EC's) investigation into Microsoft's practices almost two years ago. Google and Mozilla joined the investigation in February.

Mozilla has put forward additional changes that it believes should be made to Microsoft's current proposals.

"A few specific changes would bring the ballot much closer to the EC's stated goals of eliminating bias," said a Mozilla spokesman.

"In particular, we believe that rotating browser placement so that no browser has an advantaged or disadvantaged position, and reducing the many references to IE on the ballot page, are each important improvements."

Google declined to comment on whether it wanted further changes to Microsoft's proposals, although reports suggest that the search giant agrees with the points raised by Opera Software.

The Microsoft proposals gained EC approval early last month, which was thought at the time to signal that the investigation was drawing to a close. However, now that Mozilla and Opera Software have raised more complaints, the battle could continue.

Under the agreement, all Windows PCs sold in the European Economic Area for the next five years will contain the proposed ballot screens.